PLAGIOSTOMA 
125 
The cast of a Z>oZm7>2rwasfoiind by Mr. Weekes, 
and is figured under the name of D. nodosum in 
Sowerby’s Mineral Conchology. The Ammonites 
are not so abundant in the upper divisions of the 
clialk, as in the inferior strata hereafter to be noticed. 
Several large species, however, occur, viz. A. per- 
ampliis, Lewesiensis^ and cafinus ; and some that 
are j)eculiar, A. TT^oollgari, and nnvicularis. 
Among the Concliifera, the Terebratulm, Inoce- 
rami, and Plagiostoma, are the most numerous ; of 
the latter, P. spinosum is a very remarkable and 
peculiar species. It is readily distinguislied from 
the other shells of the chalk, by the long slender 
spines attached to the upper valve. 
