On Fresh-water Entomostraca. 21 



the statement of Prof. Weissmann, this seta is very strong, 

 spiniforin, and coarsely denticulated anteriorly. 



The tail agrees in its structure with that in most other 

 species, its outer part beyond the anal opening (fig. 4) being 

 conically tapered, and provided on each side with 10 — 12 

 denticles, the outermost of which is bidentate, whereas the 

 others are extremely delicate, squamiform and finely ciliated 

 on both edges. The terminal claws are perfectly smooth, 

 without any trace of secondary teeth. 



The ephippium (fig. 5) is of an oval or somewhat 

 semilunar form, and has the surface very coarsely reticulated. 

 It contains, as in M. paradoxa, 2 egg-ampullæ, which are 

 somewhat obliquely disposed, the one behind the other. 

 Before the ephippium is detached from the shell, [however, 

 the 2 winter-eggs occupy a rather different place, being, as 

 shown in the succeeding species (see PI. 4, fig. 2), juxtaposed 

 in the anterior part of the matrix; and in a lateral view of 

 the animal it therefore appears as if only a single ovum 

 were present. 



The adult male (figs. (5, 7) is rather inferior in size 

 to the female, scarcely exceeding a length of 0,80 mm., and 

 exhibiting a very different appearance. 



The shell is much narrower, its dorsal part not being 

 at all expanded; and the posterior extremity appears, in the 

 lateral view of the animal, obtusely truncated, forming above 

 almost a right angle. The inferior edges of the valves are 

 densely clothed with fine hairs, which, in their anterior part, 

 assume a fur-like appearance. 



The head looks very different from that in the female, 

 being much longer and more erect. It gradually tapers 

 towards the front, which appears obtusely truncated and 

 defined above by a very slight sinus. The inferior edge of 



