(XXXVI) | CRUSTACEA CASPIA. 331 
and nearly allied to P. bilamellata. From the latter species it may be easily 
distinguished by its far less slender form of body, by the somewhat different 
shape of the pseudo-rostral projection, as also by the structure of the uropoda 
and the telson. 
Description of the female, 
Adult ovigerous specimens scarcely attain a length of 5 mm, and this 
species is thus much inferior in size to P. bilamellata. 
The general form of the body (see figs. 1 and 2) is nöt nearly so slender 
and elongated as in that species, and its 2 chief divisions are also less sharply 
marked off from each other. The anterior division of the body appears of an 
oblong, or somewhat club-shaped form, being scarcely at all attenuated in 
front, and having the dorsal face but slightly arched. 
The carapace about equals in length the exposed part of the trunk, and 
exhibits, as seen laterally (fig. 1), an oval quadrangular form, being rather 
deep and somewhat truncated in front. As seen from above (fig. 2), it is 
nearly of equal breadth throughout. The branchial regions are well defined, 
having along their most prominent part a low crest, which is suddenly bent 
downwards anteriorly, and thus marks these regions sharply off from the 
gastric area. The latter has, as in P. bilamellata, 2 longitudinal keels, which, 
however, are less distinctly defined, and terminates with a very short and 
broad ocular lobe, transversely truncated in front (see fig. 3). The pseudo- 
rostral projection appears, when the animal is viewed from the side (fig. 1), 
as a very slight and obtusely rounded prominence in front of the ocular lobe. 
In a dorsal view (figs. 2 and 3), the projection is found to be, as in P. bila- 
mellata, deeply cleft in the middle by a rather narrow incision, its lateral 
parts meeting only directly in front of the ocular lobe by 2 small transverse 
apophyses. The antero-lateral corners are nearly rectangular, and defined 
above by a very slight sinus, the edges of which, as also those of the lateral 
half of the pseudo-rostral projection and of the dorsal crests, are minutely 
serrulate. The inferior edges of the carapace have their greatest curvature 
about in the middle. 
The free segments of the mesosome are quite evenly vaulted above, and 
less sharply marked off from each other than in P. bilamellata. They suc- 
cessively decrease in depth posteriorly, the last segment being comparatively 
small, with the epimera evenly rounded. 
The metasome does not exceed in length the anterior division of the 
body, and has the segments simply cylindric, though, as usual, sharply de- 
fined from each other. 
The integuments are not very strong, and exhibit, as in P. bilamellata, 
everywhere a distinct squamous structure. 
Melanges biologiques. T. XIII, p. 495. 
