4. Geoteuthis.
S. Sepia.
6. Coccoteuthis.
7. Spirulirostra.
8. Beloptera anomala.
apex, and furnished with two converging ridges on its dorsal side ; the external surface, however, is horny (or chitinous), like the pen of the Calamary. These chambered shells occur in great numbers, and are so like the phragmoconet3 of the associated Belemnites, both in structure and proportions, that they were originally described by me as and I still view them as evidences of the close affinity of the cephalopod possessing them to the true Belemnite : hitherto they have only been noticed in the laminated Oxford clay of Wilts, and the equivalent lithographic shales of Solenhofen.
Species of Belemnite are found in all the oolitic and cre taceous strata, from the lowest liar to the upper chalk. In its ordinary imperfect state, it is a cylinder pointed at one end (fig. 22, 1), and truncated or excavated by a funnel shaped cavity (alveolus, ib. p) at the other, and has a radiating fibrous structure, with less distinct concentric laminas of growth. But even this " guard," which corresponds simply to the "mucro" of the cuttlebone (ib. 5), exhibits such remarkable modifications of form, that nearly 100 species have been founded upon no higher evidence. In some Belemnites of half an inch diameter, the guard is scarcely an inch longer than the phragmocone, whilst in others it attains a length of ten inches, and is tubular, as in B. acuarius. Some are fusiform, others laterally compressed ; some have a longitudinal groove extending from the apex along the upper or under side, and in others the apex is furrowed laterally as welL The Belem nites of the chalk have been called Belemnitellce (d'Orb.), because they have a slit in the ventral side of the alveolar border of the guard ; their external surface also exhibits more distinct traces of vascular impressions.
Specimens of Belemnite have been discovered in which the guard had been broken during the lifetime of the animal ; but the broken portions, being held together by the investing orga nised integuments, had been re-united by the deposition of new layers of the fibrous structure peculiar to the guard. Several examples of Belemnites, with the apex injured and healed during life, are preserved in the British Museum. In all perfect Belemnites, the alveolus is occupied by a pivragmo cans (fig. 22, p), with tender nacreous walls and septa, terminating in a minute globular ape; and perforated by a ventral siphunele (fig. 22, z). The last chamber is rarely preserved, and appears to have thinned off into a mere horny sheath, with sometimes two pearly bands like knife-blades on the dorsal side. It must have been sufficiently capacious to contain all the viscera. The ink-bag has been very rarely found, and is even smaller than in the last genus, as if in relation to the more greatly developed shell.
The Conoteuthis (fig. 22, 3) of the Gault has an oblique phragmocone, with a very thin shell, and seems to have been attached to a slender style, like the funnel-shaped appendix of the gladius in the recent sagittated Calamary.
Mr. Dana has described, under the name Helicerus Fugi ensis, a belemnitoid fossil from the " slate" rock of Cape Horn. It is half an inch in diameter, has a thick fibrous guard, and the slender phragmacone terminates in a fusiform spiral Subjoined is a table of the extinct genera of the mollus cous province :— BRAcmOrODA.—Trigonosemus, Lyra, Magas, Rhynchora, Stringocephalus, Meganteris ; Spirifera, Cyrtia, Suessia, Athyris, Merista, Retzia, Unites ; Camaro phoria, Porambonites, Pentamerus, Atrypa, Anoplotheca ; Orthis, Orthisina, Strophomena, Koninckia, Davidsonia, Calceola ; Producta, Chonetes, Aulosteges, Strophalosia ; Trematis, Siphonotreta ; Obolus.
GAsTERoPona.—Bellerophon, Porcellia, Cyrtolites, Ecculiom phalus ; Rimella, Hippocrena, Alaria, Spinigera, Am berlya ; Leiostomus, Strepsidura, Purpurina, Columbel lina, Borsonia, Conorbis ; Euspira, Naticopsis, Globulus, Deshayesia, Loxonema, Macrochilus ; Diastoma, NerinEea, Brachytrema, Ceritella, Vicarya, Scoliostoma, Proto, Holopella, Catantostoma, Naticella ; Platyceras, Metop toma, Hypodema, Deslonchampsia ; Euomphalus, Ophi leta, Phanerotinus, Serpularia, Discohelix, Platystoma, Crossostoma, Pleurotomaria, Murchisonia, Polytremaria, Cirrus, Trochotoma, Platyschisma, Scalites, Rhaphi stoma, Holopea, Maclurea ; Neritoma, Velates, Pileolus ; Helminthochiton ; Lychnus, Dendropupa, Ferussina ; Cylindrites, Acteonina, Acteonella, Cinulia, Globiconcha, Varigera, Tylostoma, Pterodonta, Volvaria, Chilostoma ; Vaginella, Theca, Pterotheca, Conularia.