1888.] AUSTEALIAN CLADOCEEA. 27 



somewhat prominent anterior to the middle, whence they ascend 

 obliquely to the point where the dorsal edge terminates, forming 

 at some distance from this point a very slight curve. The head 

 is comparatively large, semierect, and obliquely triangular in 

 form, with the dorsal edge evenly curved and terminating infe- 

 riorly with a somewhat prominent, though obtuse, rostral pro- 

 jection, to which the antennulae are appended. The ventral edge 

 of the head is somewhat irregularly indented and joins imme- 

 diately the base of the labrum. There is no dorsal impression 

 between the head and carapace. Above the base of the antennae 

 a very slight fornicate edge may be distinguished joining the 

 carapace at the point where the free edges of the valves take 

 their origin. — When viewed dorsally the animal appears ra- 

 ther compressed; except when loaded with eggs or embryos; in 

 the latter case (see fig. 2) the dorsal part of the carapace ap- 

 pears rather dilated, with the sides bulging out in the middle. 



The shell is obscurely reticulate and exhibits on the dorsal 

 surface of the head a more or less distinct squamous sculpturing, 

 the squamules projecting somewhat posteriorly and thus giving 

 to the dorsal edge a minutely serrulate appearance. The dorsal 

 edge of the carapace, on the other hand, appears, — at least 

 in fully developed female specimens — quite smooth, without 

 any trace of the finely denticulate structure characteristic of the 

 European species M. laticornis. The ventral edges of the valves, 

 as in the other species of the genus, are slightly serrate, and 

 moreover armed with slender movable spines, arranged in a 

 double series, those of the inner row being more or less strongly 

 inflexed, the others freely projecting from the valves inferiorly. 



The eye, located at some distance from the rostral projec- 

 tion close to the dorsal edge of the head, is rather large, with 

 numerous crystalline lenses imbedded in a dark pigment, 



The ocellus, on the other hand, is very small, of irregular 

 quadrangular form, and located close to the apex of the rostral 



The antennulae, as in the other species, are movably inserted 

 to the tip of the rostral projection, from which they, as it were, 



