96 BLUE CHALK MARL. 



surface of the casts, are seen small and close transverse rugae." The 

 specuuens seldom exceed 1-5 inch in length, and are found in every locality 

 of the blue marl. 



The figure is from an argillaceous cast, in which the pearly covering 

 of the shell is preserved. 



28. Inoceramus . Tab. xix. fig. 20. 



Other species of this genus, occur at Ringmer and Norhngton, but in 

 too mutilated a state to admit of description. The beautiful specimen 

 deHneated,fig. 20, tab. xix. is remarkable for possessing the fibrous structure 

 observable in the Inocerami of the chalk ; and for retaining its crenulated 

 hinge ; this shell is probably a variety of I. concentricus. 



29 and 30. Tab. xix. figs. 7 and 8, represent two argillaceous casts of 

 bivalves from Norlington, the genera of which cannot be correctly ascer- 

 tained. The former is a front view of a cordiform bivalve, perhaps related 

 to the Isocardije ; the latter probably belongs to the genus Area : they are 

 both solitary examples. 



Crustacea. 



The remains of this order of animals, are so exceedingly rare in the 

 blue marl, that with the exception of a few fragments, the dehneations in 

 tab. xxix. comprise every specimen that has occurred in Sussex. 



To the kindness and Uberality of William Elford Leach, M. D. of the 

 British Museum, who did me the favour to compare them with the recent 

 species, to which they are most nearly related, I am indebted for the 

 following identification of their genera. 



31. Tab. xxix. figs. 7, 8. 14. "A species of a new genus of the family 

 Leucosiados *, nearly related to the genus Arcania." Dr. Leach. 



In these specimens the shell or crust of the thorax alone remains. It 

 is of a suborbicular form, rather inflated, obscurely trilobate, with twelve 

 or thirteen aculeated tubercles ; the margin is dentated. 



* The recent Leucosiadce have two or four small quadriarticulate antennae inserted between 

 the eyes. The tail is naked ; they have eight legs, all furnished with claws ; and two chelate 

 hand claws. Rees' Cycloped, Art. Cancer. 



