PROCEEDINGS OF SECTION D. 47] 
On the second, third, fourth and fifth there are appendages, 
diminishing in size towards the posterior end, and consisting of a 
protopodite of two segments, a very small coxopodite and longer 
basipodite, surmounted by an exopodite and endopodite, which 
are similar in form and almost of the same size, the endopodite 
being generally rather the smaller, except on the fifth segment. 
Each has the form of a narrow, flat, membranous plate, bordered 
by more perfectly calcified serrations, from which arise large 
plumose sete forming a close fringe to the appendage. The 
appendages of the sixth segment forming, with the telson, the tail 
tin, have much the same shape as in Astacus. 
Gills —The gill formula is as follows :— 
Arthrobr. 
Thore. segt. Podobr. ant. post. Pleurobr. 
Ihe af ep. s0c 0 0 0) 
II. 1 1 0 0 
III. 1 1 A ) 
IV. 1 i! 1 0 
Ve i 1 it 1 
Ve 1 1 1 1 
VII. iL 1 1 rud. 1 
VIII. 0 10) 0) 1 
6+ ep 6 4+rud. 4=20+rud.+ep. 
This differs from the formula of Astacus, in having the posterior 
arthrobranch on the 7th segment rudimentary, and all the pleuro- 
branchs fully developed. 
The podobranchie have a somewhat complicated structure. 
The stem, or main axis, arises from a broad basal piece directed 
backwards, and covered with plumose setz, with hooked ends. 
This is continued upwards as a narrow posterior wing to the stem, 
which is covered elsewhere very closely with branchial filaments. 
From its inner side a flat plate projects, lying between the 
arthrobranchs and covered, though much less densely than the 
rest of the gill, with branchial filaments. It is very small and 
narrow on the posterior podobranchs, those of segment 7, and 
gradually increases in size in the more anterior ones, in which 
it finally extends nearly the whole length of the gill. The 
epipodite on the first thoracic segment is a flat plate, furnished on 
the posterior surface with branchial filaments resembling the 
inner projecting plate of the podobranchs. 
In front of each podobranch is a tuft of coxopoditic sete, like 
those of Astacus, but much smaller, and provided with hooks. On 
the posterior edge of each segment there is a small flat plate, fringed 
with hooked setz, and formed from the membrane of the joint. 
The arthrobranchize consist of a simple stem, with very 
numerous filaments, except along the posterior inner surface, 
