On Fresh-water Eiitomostraca. 39 



and terminates in an acute rostrum, somewhat shorter than 

 in that species. 



The surface of the shell is sculptured with distinct, 

 though not very sharply marked, longitudinal striæ, which 

 are less closely set than in the preceding species, their 

 number being f rom 14 to 15 on each side. The inferior edges 

 of the valves are, as usual, densely ciliated. 



The eye is well developed, with distinct, though small 

 crystalline bodies. 



The ocellus is much smaller than the eye, and plac3d a 

 little nearer to it than to the tip of the rostrum. 



The antennulæ exhibit the usual narrow subfasiform 

 shape, and do not extend to the tip of the rostrum. 



The antennae are less powerful than in the preceding 

 species. 



The lamellar expansion of the labrum is rather large, 

 aud has the edge perfectly smooth. 



The tail (fig. 4) closely resembles that in A. lœvissima, 

 being comparatively short, and of uniform breadth. It is 

 transversely truncated at the tip, with the posterior corner 

 well defined and somewhat produced. The post-anal angle 

 is distinctly marked, though not very prominent, and 

 the posterior edge below it appears perfectly straight, car- 

 rying a double row of very small, hair-like denticles, 10 — 12 

 in each row. As in the preceding species, there is on each 

 side an additional lateral row of extremely delicate, some- 

 what squamiform spinules. The terminal claws are con- 

 siderably elongated, and each exhibit at the base a well- 

 marked secondary denticle. 



Occurrence. — Some few specimens of this form, all 

 of them females, were found in the sample at first received 

 from Prof. Ramsay, and taken from the "Waterloo Swamps. 



