As the means by which many of the ifollusca bore into the rocks in which they reside are at present unknown and are matters of much discussion, the conclusions at which Mr. Darwin has arrived with read to the species of Lithutrya are of high interest. After describing accurately the structure of the valves, the peduncle, the muscles of the peduncle, the basal calcareous cups or discs, and the internal structure of the cup, he concluded :—" The several species occur imbedded in soft calcareous rocks, in massive corals, and in the shells of Mollusca and of Cirripedes. It has been doubted by several naturalists whether the basal calcareous cup at all belongs to the Lithotrya ; but after the foregoing microscopical observations on its structure it is useless to discuss this point. So again it has beeu doubted whether The cavity is formed by the eirripede itself; but there is so obvious a relation betweeu the diameters of specimens of various sizes and the holes occupied by them that I can.cutertain no doubt ou tali/. head. The holes moreover are not quite cylindrical, but broadly oval, like the section of the animal. The simple fact that in this genus alone each fresh shay layer round the bases of the valves, and therefore at the widest part of the capituhun, is sharply toothed; and secondly, that in this genus alone a succession of sharply-serrated scales, on the upper and widest part of the peduncle, is periodically formed at each exuviation, and that con sequently the teeth on the valves and scales are sharp and fit for wnring soft atoue at that very period when the animal has to increase in size, would alone render the view probable that the Lithotrya makes or at least enlarges the cavities in which it is imbedded. Although it may be admitted that Lithotrya has the power of eulargiug its cavity, how does it first bore down into the rock? It is quite certain that the Waal cup is absolutely fixed, and that neither iu form nor state of surface it is at all fit for boring. I was quite unable to answer the foregoing question until seeing the admirable figures by Reinhardt of L. Nicubarica still attached in its cavity. Subsequently 1 obtained from Mr. Stutehbury several pieces of rock completely drilled with holes, many of small diameter, by L. dorsalis; and in these 1 found numerous instances of the linear rows of little discs like those of L. Neeobarica, showing in the plainest manner that each time re new disc is formed, that is, at each exuviation, the animal moves a short step downward"; and as the lowest of these little discs in none of the burrows was placed at the very bottom, we see that the lowest point of the peduncle must be the wearing agent. In the peduncle of an Individual of L. dorsalis, nearly ready to moult, I found, it may be remembered, beneath and round the basal din, under the old membrane of the pedtmele, a new membrane studded with calcified beadle, but with the horny star-headed spines not yet developed ; whilst on the old outer coat these latter had been worn down quite smooth, and the calcified beads worn entirely away. Here then wo have an excellent rasping surface. With respect to the power of movement necessary for the boring action, the peduncle is amply furnished with transverse, oblique, and longitudinal strkelesa muscles, the latter attached to the basal disc. Iu all the Peduneulata I have reaaou to believe that these muscles are in constant alight involuntary action. This being the case, I conceive that the small blunt spur like portion of the peduncle descending beneath the basal rim of the lowest dime would iuevitably partake slightly of the movements of the whole distended animal. As soon as the Lithotrya has reached that depth which its instincts point out as most suitable to its habits, the discs are converted into an irregularly growing cup, and the animal then only increases in diameter, enlarging its cavity by the actiou of the serrated scales on the peduncle, and of the serrated lower edges of the valves of the capitulum. With respect to those reversed individuals attached with their capitultuns downwards, I suppose that the lame had crept into some deep cavity perhaps made originally by a Lithotrya, of which the rock in the specimen in question was quite full, and had there attached themselves. Finally, it appears that in Lithotrya the burrowing is simply a mechanical action : it is effected by each layer of sholl in the basal attached discs overlapping in a straight line the last-formed layer ; by the membrane of the peduncle and the valves of the capitultun having excellent and often renewed rasping surfaces; and lastly, by the end of the peduncle (that is, homologically the front of the head) thus roughened, extended beyond the surface of attachment, and possessing the power of slight movement" L. dorsal is, G. B. Sowerby. It is the Lepas dorsalis, Ellis ; Litho lepas do Mont Serrat, De Blainville. Scuta narrowly ovalapping the terga; mina internally concave ; rostrum as wide as two or three of the subjacent scales ; latera with their internal sur faces narrowly elliptical, as long as five of the subjacent scales; upper scales of the peduncle less than twice as large as those in the second whorL This species is found imbedded in lime stone at Barbadoes, Venezuela, and the Honduras.
L. eauta, Darwin, named from a unique specimen, was found imbedded in a (Ionia or Tctraclita from New South Wales.
L. Nicobarica, Reinhardt, is a rare spe cies occurring in the Nicobar Islands.
L. Ilhodiopus Darwin, is named from a specimen imbedded in a massive coral in the British Museum.
L. truncata, Darwin, found imbedded in coral rock in the Fricudly Islands and Philippine Archipelago.
L. Valentina, Darwin, from two specimens imbedded in an oyster shell, in the British Museum, from the Red Sea.
. Order IL Abdominalia.
Cirripedia having a flask-shaped carapace. Body consisting of 1 cephalic, 7 thoracic, and 3 abdominal segments, the latter bearing 3 pairs of cirri; the thoracic segments without members; mouth with the labrunt greatly produced, and capable of independent movements; oesophagus armed with teeth at its lower end ; larva firstly egg-like, without extenutl limbs or an eye; lastly, binocular, without thoracic legs.
This order contains only ouo genus and one species, Croptophialus minutes, Darwin, 1854. It is very distinct from all other Cirripodes, but more nearly allied to Akippe amongst the Lepadidce than to any other form. It bores cavities in the Cuncholepas Peruciana, and is of very minute size.
Order Ili. Apoda.
Cirripedia with the carapace reduced to 2 threads, serving for attachment. Body consisting of 1 cephalic, 7 thoracic, and 3 abdominal segments, all destitute of cirri ; mouth suctorial, with the mandibles and maxilla:, placed back to back, inclosed in a hood, formed by the union of the Labrum and palpi ; metamorphoses unknown.
This order, like the last, contains only one genus and species, Protco lepas birincta, Darwin, 1854. It was found parasitic within the sac of another Cirripede in the West Indies. Until most closely examined the Proteukpas would never have been imagined to have belonged to the class of Cirripedia. In external appearance it resembles the larva or maggot of a fly ; its mouth is unlike that of any known type in the articulate kingdom.
Poaril Cirripedia.
As with the recent so with the fossil species of this family, we are most indebted for our knowledge of them to the exhaustive labonrn of Mr. Darwin, whose recent investigations on this subject have thrown all others into the shade. The result of his inquiries into the extinct history of the Cirripedia has been given in a work published by the Paheontographical Society, which, although more immediately intended to illustrate the fossil Pedunculated Cirripedes of Great Britain, embraces an outline of the whole subject as far as it is known. In our remarks we shall follow Mr. Darwin. " No true Sessile Cirri pede," he says, "has hitherto been found in any Secondary formation. Considering that at the present time many species are attached to oceanic floating objects, that many others live in deep water in con gregated masses, that their shells are not subject to decay, and that they are not likely to be overlooked when fossilised, this seems to be one of the cases in which negative evidence is of considerable value." Often observers have searched with great care amongst the Secondary rocks and have met with nothing that bear the characters of the Balanidce of the present day. The Sessile Cirripedes are first met with in the Eocene deposits of the Tertiary formations, and subse quently often in abundance in the same formation. They appear how ever never to have abounded so greatly as at the present time, so that Mr. Darwin says, " The present period will hereafter apparently have as good a claim to be called the age of Cirripedes as the Palaeozoic period has to be called the age of Trilobites." He adds, "There is one apparent exception to the rule that Sessile Cirripedes are not found in Secondary formations, for I am enabled to announce that Mr. J. de C. Sowerby has in his collection a Verruca from our English Chalk; but this genus, though hitherto included amongst the Sessile Cirripedes, must, when its whole organisation is taken into considera tion be ranked in a distinct family of equal value with the Balanicke and Lepadidtr, but perhaps more nearly related to the latter than to the Sessile Cirripedes." The oldest known Pedunculated Cirripede is of Pollicipes discovered by Professor Buckman in the Stonesfield Slate in the Lower Oolite, and two species of the same genus have been described by Mr. Morris from the Oxford Clay in the Middle Oolite. No Cirripede has yet been found in the Upper Oolite, or in the Wealden Beds. During the development of the great Cretaceous system, the Lepadidce arrived at their culminating point. At this time there existed 3 genera and at least 32 species, some occurring at every stage of the system. In addition to the species described there aro several doubtful, and by future research many more will undoubtedly be added to the present list.
Although rich in species, the individuals in the Chalk oceans seemed to have been rare, if we may judge from the few remains of particular species that exist in any one collection. It is not always the case that a great variety of species is attended with a multiplicity of individuals, although that is frequently observed.
In the Eocene, Miocene, and Pliocene Tertiary deposits, Mr. Darwin has met with but two species of Scalpdluni and two of Pollicipes, distinct from recent forms. Two or three species are doubtful. It is a singular fact that, widely distributed as are the species of Lepas at the present day, and the frequency of the individuals, not a single valve known certainly to belong to this genus or to any of the closely allied genera, has hitherto been found fossiL The following is a table of the species described in Mr. Darwin's monograph :— CIS, a genus of Coleopterous Insects of the family Ptinidce (Leach). They are minute Beetles which infest the various species of Boleti. They are of an oblong nearly cylindrical form, and generally of a brown colour : their tarsi are 4-jointed, and the anteurue have the basal joint large, and the three apical joints forming a club. Four teen species have been discovered in this country, the largest of which is scarcely one-eighth of an inch in length.