322 UPPER, OR FLINTY CHALK. 



The external antennae are long, filiform, and setaceous, and are placed on 

 squamous peduncles ; the inner pair have not been discovered. The two 

 chelate hand-claws are equal, and have their surface muricated, or beset 

 with short erect spines. The pincers are very long, not muricated, but 

 marked with three or four longitudinal, punctated furrows ; each finger is 

 armed with a row of obtuse, cylindi'ical spines, which are mutually re- 

 ceived and inserted, when the claws are shut. The claws, including the 

 pincers, are equal to twice the length of the thorax. 



There are five legs on each side ; the anterior pair is didactyle ; the 

 others appear to terminate in swimmers or paddles, but this circumstance 

 cannot be accurately determined. The abdomen is composed of six 

 granulated arcuate segments. The tail is fohaceous, marginate, granu- 

 lated, and has a few longitudinal ridges ; but the only known specimen 

 (Tab. XXX. fig. 1.) does not exhibit the entire form. 



This species appears to be distinguished from the recent animals of 

 the genus, by the dorsal ridge and lateral sulci of the thorax ; the great 

 length and straightness of the pincers; and the peculiar form of their 

 spinous processes. 



In naming this fossil in honour of Wm. Elford Leach, M.D. of the 

 British Museum, I am desirous of testifying the high respect which I en- 

 tertain for his talents as a naturalist, and particularly for his excellent 

 systematical arrangement of the crustaceous animals. 



Tab. xxix. figs. 1, 4, 5. The chelate claws of A. Leachii. 



fig. 4. is the largest example hitherto discovered. 



fig. 1. A fragment of the pincers of the preceding specimens. 



fig. 5. A block of chalk, containing part of a claw, leg, 



and several detached spines; fragments of a fish are 

 attached to the upper part of this specimen. 

 Tab. XXX. fig. 2; two chelate hand-claws, attached to the chalk in which 

 they were imbedded. 



Tab. xxxi. fig. 1 : on the left of this specimen, part of the thorax is 

 attached; and on the right, a hand-claw deprived of 

 one of its pincers. 



