160 Transactions.—Zoology. 
is composed appear to be modifications of the naked jointed set already 
described. There is a joint about the middle (pl. XXL, fig. 4 a). The 
basal part is quite naked, the distal half is naked until some little distance 
past the joint, but is then thickly covered with short simple filaments. 
These filaments extend nearly to the end of the seta, which is hooked (b). 
In the concave portion of the hook there is often a slight projection (e). 
The inner surface of each branchiostegite is thickly covered with jointed 
sete. In these the filaments on the distal half are less conspicuous than 
in the coxopoditie sete ; in this point they are intermediate between the 
coxopoditie sete and the ordinary jointed sete found on the chele, etc., but 
they resemble the coxopoditic setze in having their extremities hooked. On 
the inferior edge of the branchiostegite there is a row of sete hanging 
downwards. These are similar to those found on the inner surface of the 
branehiostegite except that the extremities are not hooked. I am quite 
ignorant of the function of all the hooked set that I have described ; they 
appear to have something to do with the respiratory organs, as it is only 
those in immediate connection with the respiratory organs that are hooked. 
Circulatory system.—The circulatory system, as far as could be seen . 
without injection, does not appear to differ in any important particular 
from that of Astacus. The heart is of similar shape and lies behind the 
stomach and above the intestine and reproductive organs. The abdominal 
artery was readily seen running along the dorsal surface of the abdomen 
and giving off branches in each somite. The sternal artery was also seen 
passing vertically downwards to the ventral surface of the animal, where it 
divides into an anterior and a posterior branch. The arteries arising from 
the anterior portion of the heart are smaller and are not so readily seen. 
Alimentary system.—The general course of the alimentary canal is, as 
might have been expected, very much like that of Astacus. The cesophagus 
is large in section and expands almost immediately into the capacious 
stomach. The stomach consists of two parts, the cardiac and the pyloric, 
the former of which contains a gastric armature, which is fully as compli- 
cated as that of Astacus. It is formed on the same type, so that the same 
names can be used in describing the various parts. The anterior edge of 
the cardiac ossicle (pl. XX., figs. 5 and 6 c) is much more convex than in 
Astacus; and the remaining part is divided into four portions, as shown in 
fig. 5. Thé urocardiac process (ue) is more or less oblong, not quite twice 
as long as broad, with the sides slightly concave, at the posterior end are 
two rounded prominences. The median tooth (mt) is dense and hard; the 
end curves forwards and is bifurcated at the summit. The urocardiac 
' process and the median tooth are united by the prepyloric ossiele (pp) to 
the pyloric ossiele (p) in the same way as in Astacus. The pterocardiac 
