PROCEEDINGS OF 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. Wright gave a general 
sketch of the organization of the Gasteropoda 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 
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 in 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 
2 p 
VOL. in.— no. xx. 
