344 CRETACEOUS CRUSTACEA. 
Notes on the Crustacea of the Chalk Formation. By Prorrssor 
Tuomas Be tt, Sec. R.S. 
CRUSTACEA. 
MACROURA. 
Paleastacus Dizoni, Bell. (Tab. XXXVIII*. figs. 1, 2, 3, 4, 5.) 
The unique and beautiful fossil, represented of the natural size in figs. ] & 2, 
appertains to a species of a Macrourous genus nearly allied to Astacus and 
Homarus, to which I have applied the name of Paleastacus Dixom. It is 
characterized by the extremely tuberculous surface of the whole of the crust, 
passing into spines on the sides of the abdominal segments. ‘The transverse 
division of the exterior caudal lamina was so slightly indicated in this specimen 
as scarcely to be recognizable ; but the whole character of the animal points out 
clearly its close affinity to the typical Astacide. The division in the caudal 
lamina above adverted to is perhaps to be traced in fig. 5. 
The carapace in this species exhibits the nearly cylindrical form of the lobster 
and the crayfish, but is a little more contracted anteriorly ; the rostrum is tri- 
angular and slightly spinous at the sides, as seen in figs.1 & 3. The different 
kinds of tubercles are very remarkably distinguished on different portions of the 
carapace, and are separated by a distinct line of demarcation. ‘Thus the lateral 
and latero-posterior portion, comprising the whole of the branchial region, is 
covered only with small, close, and low tubercles; whilst the anterior and 
median portion, covering the hepatic, gastric, genital and cardiac regions, has in 
addition to the slightly tuberculated surface, a considerable number of large and 
distinct tubercles. The claws, which are very large in proportion to the size of 
the animal, are covered with still larger and more elevated tubercles than those 
of the carapace. The hand is robust, rounded, and almost ventricose ; and the 
fingers meet only at the points, the immoveable one being straight and the other 
considerably curved. Judging from the fragments of the smaller legs which 
remain, these were doubtless, as in the other species of the family, slender and 
filiform. The segments of the abdomen are studded, particularly at the sides, 
with strong, almost spinous tubercles; the terminal segment, or middle lamina 
of the tail, is rounded at the extremity and tuberculated over the surface. 
