PROCEEDINGS OP SOCIETIES. 277 



and eight species are peculiar to the chalk. After the deposition of the secondary 

 rocks they all became extinct. As illustrative of the history and organization of 

 the Foraminiferous Cephalopes, the lecturer described the nummulite which was 

 so abundant in some localities ; a limestone rock, composed almost entirely of this 

 fossil, was that of which the Pyramids are built. Mr. Weight gave a general 

 sketch of the organization of the Casteropoda and Conchifera, and explained the 

 character of some of the genera of these classes, which are so very abundant in 

 our neighbourhood ; and he detailed the striking disparity between the Herbivo- 



, rous and Carnivorous trachelopodes in the older rocks, and showed that the part 

 which was once played by the Cuttlefish tribe, in checking their increase, was, 

 after the extinction of the Ammonitidce, performed by Carnivorous Casteropods, 

 singularly adapted to wage war upon the almost defenceless Herbivora. The 

 lecturer gave a general sketch of the organization and classification of the Arti- 

 culated animals, and observed that, although above a hundred thousand species 



I of insects are deposited in our museums, and which number was supposed to be 



| far short of the number existing, yet this extensive class were almost altogether 

 absent in the stratified rocks ; fossil insects are found in the coal formations and 



| in the oolitic system ; and above sixty genera are known to exist in the tertiary 

 strata. The class Crustacea next engaged the lecturer's attention, and he demon- 

 strated the fossil Crabs, which are found in such abundance in the London clay 

 of the isle of Sheppey, from numerous specimens on the table, from that locale. 

 The genus Astacus was described, and the species from our neighbourhood shown 



- which had lately been figured in the Illustrations of the Geology of Yorkshire. The 

 singular and ancient family Trilobitidce were described, and their organization 

 and classification amply illustrated by numerous specimens and drawings, repre- 

 senting some of the most interesting genera. The faculty which Calymene 

 enjoyed, of rolling itself into a ball like the Glomeris and Armadillo, was alluded 

 to; and the affinities which exist between the Trilobites and other isopod- 

 ous Crustacea satisfactorily demonstrated. The fossil Cypris was described, 

 and the history of the species abundant jn our neighbourhood detailed, to 

 explain the wonderful abundance of the horny shells of these microscopic 

 Entomostraca in some tertiary fresh-water formations. The character of the 

 genus Limulus was described, and the lecturer entered upon the history of Fossil 

 Radiata. He demonstrated the organization of the Echinodermata, and showed 

 the interesting gradations of structure observed in this class, from the globular 

 shell of the Echinus to the radiated form of the Starfish : this was rendered very 

 familiar by dividing the skin of an orange into five segments, which, retained in 

 situ, produced a form analogous to the Common Urchin ; but which, when folded 

 down, assumed the characteristic shape of the Starfish. The gradations of struc- 

 ture presented by the different genera of the Stellirida were next described, and 

 VOL. III. — no. xx. 2 p 



