1835.] 



CLADOCERA. 



31 



a great part of the mandibles, and inferiorly form a broadly 

 rounded corner. The ventral edges are almost straight, and 

 fringed with short hairs ; they are not distinctly marked off from 

 the posterior, which are slightly incurved in their upper part. 



As regards the sculpture of the snell, no trace can be detected 

 in other places, except on the valves, where delicate, obliquely 

 transversal striæ, somewhat flexuous and partly anastomosing 

 with each other, may be readily observed. The shell-gland forms 

 a simple coil of canals in the anterior part of the valves. 



The eye — placed within the anterior projecting part of 

 the front — is comparatively large, though somewhat smaller 

 than in M. brachiata. It is provided with numerous refracting 

 corpuscles, forming a clear zone round the dark pigment. Of 

 the ocular spot, no trace whatever can be detected. 



The antennulæ exhibit the structure characteristic of the 

 genus, projecting freely, and very movably jointed to the inferior 

 part of the head. They are narrowly fusiform, and densely 

 fringed along the posterior border with rather long and delicate 

 cilia. The tentacular seta, affixed about in the middle of the an- 

 terior margin, is rather long, whereas the apical sensory papillæ 

 are exceedingly small. 



The antennæ are very powerfully developed, and agree 

 precisely in their structure with those in M. brachiata, the num- 

 ber and arrangement of the natatory setæ being exactly the same. 



This would also appear to be the case [with the oral parts 

 and the legs. 



The tail (see Pl. 6, 'fig. 1), as in the other species of 

 the genus, cannot be entirely retracted within the carapace, 

 a more or less considerable part of its terminal section being 

 invariably exposed behind. As to form, it corresponds very 

 nearly with that in M. brachiata. A single conical dorsal process 

 occurs somewhat far out anteriorly, admitting of being closely 

 applied against an internal crest of the carapace, and thus closes 

 up the matrix posteriorly. The terminal section is rather produced, 

 tapering rapidly toward the apex, which is conically pointed. 

 Its dorsal margin constitutes, a little beyond the middle, a broadly 



