The species are apparently confined to the wanner seas, the Mediterranean being the locality of the lowest temperature where any of them have been hitherto found.
Fossil Chatilidcr.
The fossil species of Chania are numerous, and occur in the supra cretaceous groups, particularly in the enbappenine beds, and those of Bordeaux and Dax ; in the Cretaceous group ; end also in that of the Oolite. According to G. B. Sowerby, they are found in the London Clay, and Calcaire Greasier, also in the Chalk and Greensand. Deshnyes, in his tables, gives fifteen living species, and twenty fossil (tertiary), occurring in the Pliocene, Miocene, and Eocene periods. Of these he makes four, namely, C. grypholdes, C. crenulata, C. sinistrorsa, and a new species, both living and fossil ; the localities for the living (with the exception of crrnulata, from Senegal) being the Mediterranean Sea. The species found in more than one Tertiary formation ho makes a echinulata, C. rustica, and C. lamellosa ; and gives the follow ing number of species in the localities here mentioned :—Four in Sicily, four in Italy (subappenine beds), one at Bordeaux, three at Dax, three in Touraine, two at Vienna, two at Angers, nine at Paris, one at London, and two at Valognes. In the fossil list of his edition of Lamarck (1835), Deshayes enumerates only thirteen fossil species, and of these he makes C. gryphina include C. einisiroila ass synonym, observing in a note that he knows the living analogue as existing in the Sicilian seas, and that the species No. 3 (C. lacernata) is a variety of this, while the valves cited as belonging to the environs of Angers belong to another species. C. echinulata he identifies with C. asperella now living in the Mediterranean. C. unicornaria, be observes, was formed for a variety of C. gryphina, with very large umbones; and he suggests the necessity of uniting C. gryphina, lacernata, and C. unicornaria in one species. Nilsson names C. cornet Arita* (Diceras arietina 1), Kjuge ; Morby, Sweden ; and C. laciniata, Kjuge ; Bats berg ; Morby, Sweden ; and Mantell, an undetermined species from the Chalk, Sussex. Phillips names Chaim mime, or Gryphera mime (the genera are sufficiently different, by the way), from the Coral Oolite and Calcareous Grits of Yorkshire. Smith, Chama (1) craua from the Bradford Clay. Thurman, C. Bernojurensis, from the Calca
reous Grit, Barnes° Jura ; and Lonsdale, an undetermined species from the Cornbrash Forest Marble, and Bradford Clay, Wilts.
Clavier says that the Dicerata do not appear to differ from the Chama in anything essential ; only their cardinal tooth is very thick, and the spirals (=bones) of their valves are sufficiently projecting to remind the observer of two horns. G. B. Sowerby thus writes : " On account of the similarity between this genus (Chema) and Diceras wo shall be expected to explain the characters by which this latter is distinguished from Chaste, with which Indeed it is arranged by Bru guiere; these, according to Lainarek, are the large, conical, diverging, spiral umbones, and the large, concave, subauriculate, prominent tooth in the large valve of Dieerus. Not having ourselves soon the hinge of Diceras, we will not venture to offer an opinion ; but, judg ing from the specimens we possess, we see in Diceras a sort of con necting link between Isocardia and Chama, having both the umbolica free and Involute, and being moreover a nearly equivalve shell, like lsocardia ; but being attached by one valve, and not quite equl valve, in these respects resembling Chama." Rang observes : "This genus is very imperfectly known, without doubt, but nevertheless one may well believe that it is very near to Chasta." Defruuace enumerates five species. Deshayes does not give it as a genus in his tables, and in his last edition of Lamarck only two species are recorded, Diceras arittina (Lam.), the typo from Mont Salve and the neighbourhood of St. 3lihid, and Diceras sinistra (Dealt.), from the superior Oolito in the vicinity of the last-named place.
• Rang would place next to Diceras the genus Caprice of D'Orbignv senior ; and he is of opinion that if that zoologist would publish his discoveries on these interesting shells, the genus would be gene rally adopted. The genus Ichthyo sarcolite, which has been always classed with the Cephalopods, might, he thinks, belong to a bivalve approximating to Caprice.
Deshayes, he says, communicated to him the same idea. But the butt named author does not notice the genus when treating of Diceras in the last edition of Lamarck.