CRETACEOUS PERIOD. 475 



(c.) Lamellibranchs. — Species of Gryphcea, Exogyra, Inoceramus, Gervillia, Trigo- 

 nia, — all extinct; also of Cardium, Astarte, Cardita, Corbula, Isocardia, Lima, Crassa- 

 tella, Cyprina, Cytherea, Venus {?), Lucina, Panopcea, Avicula, Pecten {?), Neithea, 

 Pholas, Sporulylus, Tellina, Plicatula, and many other genera of existing seas, which 

 give a modern aspect to a conchological cabinet of the Cretaceous period. Among the 

 species of the extinct tribe of Rudistes, Fig. 862, Hippuiites Toiicasianus D'Orb., from 

 the Upper Cretaceous, one of the most common species of southern Europe ; Fig. 862 a, 

 H. dilatatus Defr., vertical view, showing the interior of the lower conical valve, from 

 the Lower Cretaceous; Fig. 863, Radiolites Boumoni D'Orb., upper valve in profile, 

 from the Upper Chalk; Fig. 864, Sphcendites Haninyhausi Desm., upper valve in pro- 

 file, from the Upper Chalk; b, c, in 863, 864, attacbments of muscles. 



(d. ) Gasteropods. — The extinct genera Xevincea, Actceonina, Actceonella, Avellana, 

 etc. The modern genera Voluta, Olivet, Fasciolakia, Ovula, Cypr^ea, Trochus, 

 Xerita, Xaiica, Mitra, Conn*, Verithium, Bulla, etc., showing a striking approxima- 

 tion to the present age, in the closing period of the Mesozoic. (The genera in small 

 capitals are some of those which are supposed to have made their first appearance in 

 the Cretaceous period.) Fig. 865, Xeiincea bisulcata D'Archiac, from the White Chalk. 

 Fig. 866, Avellana Cassis D'Orb., from the Upper Green-sand; a, outline sketch, show- 

 ing the toothed aperture. 



(e.) Cephalojwds. — Ammonites: Fig. 867, Crioceras Duvalii Leveill^, from the Lower 

 Cretaceous; Fig. 868, Ancyloceras Matheronianum D'Orb., Lower Cretaceous; Fig. 

 889, Hamites attenuatus Sow., Middle Cretaceous; Fig. 870, Toxoceras bituberculatum 

 D'Orb.; Fig. 871, Turrilites catenatus D'Orb., Gray Chalk. Also Baculites (as B. an- 

 ceps Lam., etc.). — Also Belemnitella mucronata D'Orb., a common species of the Upper 

 Cretaceous; also species of Belemnites and Conoteuthis. 



4. Articulates. — Worms of several genera. Crustaceans, of the Brachyural 

 genera, Grapsus, PodnpktJialmus, Podopilumnus, Arcania, Xotopocorystes, etc. ; and the 

 Macrural, Scyllarus, Callianassa, Pakeastacus, etc. Of the tribe of Cirripeds, Tubici- 

 neUa, Pollicipes. Also Ostracoids. 



5. Vertebrates. — (a.) Teliost Fishes. — Fig. 872, Osmeroides Lewesiensis Ag., 

 from the Chalk at Lewes, — a fish of the Salmon family (Cycloid) related to the Smelt 

 (genus Osmerus), and about fourteen inches in length. Another species of the genus, 

 from the same beds, 0. ManteUi Ag., is eight or nine inches long. There Avere other 

 Cycloids, of the genus Clupea (Herrirfg), etc. Several species of Beryx, a genus re- 

 lated to the Perch (Ctenoid), occur in the Chalk; one, B. Leicesiensis Dixon, is a 

 broad fish, six to twelve inches long; another, B. superbus Eg., sometimes thirteen 

 inches long. Ganoids were numerous in species, of the genera Belonostomus, Caturus, 

 Lepidotus, etc., besides others of the Pycnodont family, Pycnodus, Gyrodus, etc. 

 Sharks of the Hybodont family were sparingly represented: Cestraciont remains were 

 very common, especially of the genera Ptychodus and Acrodus. Teeth of Squalodonts 

 are occasionally met with, of the genera C«rcha?*ias, Lamna, Oxyrhina, Odontaspis, etc. 



(b.) Reptiles. —Fig. 873, Mosasaurus Eofmanni Mant., head from the Chalk at 

 Maestricht, one eighteenth the natural size; a species which has been found also at 

 Lewes in England. In the figure, the articulation in the lower jaw is concealed by the 

 fragment of a jaw overlying it; and hence its existence was never found out from the 

 study of the specimen. 



Leiodon, Raphiosaurus, and Coniosiurus are other genera of the Upper Cretaceous. 

 The genera Jchthijosaurus, Plcsiostums, and Pterodactylus reach even into the Upper 

 Cretaceous : Jguanodon and Teleosaurus occur in both Lower and Upper Green-sand 

 in England. 



The several divisions have the following characteristic fossils : — 



I. Lower Cretaceous. — 1. Lower Green-sand, or Xeocomian. — Holocystis elegam 

 E. k H., Toxns'er complanatus Ag., Rhynchnnella Gibbsiana Dav., R. depressa D'Orb.^ 

 Terebratuln sella Sow., Ostrea Leymerii Desh., Exngyra sinuata Sow., E. Couhmi 

 D'Orb., GerviBia nnccps Desh., Myaciies mandibula Sow., Perna MuUeti Desh., Tri- 

 gonia dcedalea Park., T. caudata Ag., Pleurotomaria gigantea Sow., Pterocera Fittoni 



