168 Mr. C. Spence Bate on the Affinity of Praniza with Anceus. 



the more continuous and less graceful outline from the anterior 

 part of the head to the posterior part of the pereion, the short- 

 ness of the pleon, and the smallness and more equal size of the 

 pereiopoda ; and in the less easy to be detected, but not less im- 

 portant facts, that the mandibles do not extend beyond the labium, 

 and the gnathopoda have but four articulations and terminate 

 in a rudimentary form. The powerful hook is wanting. One 

 of this latter species, which I shall name Edwardsii, after its 

 finder, who has been a valued correspondent during my researches 

 in this class of animals, was charged with young. It is a remark- 

 able fact, that in the young the organs generally bear a closer 

 resemblance to those of P. cceruleata than to those of their own 

 parent species. 



In the young the mandibles project beyond the labium. The 

 gnathopoda are furnished at the extremity with powerful hooks. 

 The siphon is prominent and well formed. The five conspicuous 

 segments of the pereion correspond in their relation to each 

 other, the centre one being the largest, and the posterior and 

 anterior being equal and the smallest : no fusion exists between 

 any of them. On the ventral surface of the four posterior seg- 

 ments is pendent a membranous sac. It is the monstrous enlarge- 

 ment of this sac in the development of the animal, fusing into one 

 segment and separating widely apart the three posterior pereio- 

 poda, that gives to this animal its most remarkable and peculiar 

 feature. 



In an examination of Anceus we find some points that assi- 

 milate and others that are widely distinct from the structure of 

 Praniza. The eyes are sessile and placed anteriorly upon each 

 side of the head. The cephalon is quadrate, depressed from the 

 centre to the anterior margin ; the lateral edges are raised like 

 walls on each side. 



The antennae (PL VII. fig. 3 b, c) are subequal, placed, as in 

 Praniza, at the anterior lateral angles of the cephalon, and one 

 immediately above the other. 



The labium is absent or rudimentary. 



The mandibles (d) are prominent and powerful ; they originate 

 at the anterior extremity of the cephalon, and extend horizon- 

 tally in advance of the head. 



The maxillipedes (g) consist of five articulations, a projecting 

 process arising from the basal one. 



The gnathopoda {h) consist of two articulations, one large and 

 the other very small. The large one is straight on the exterior 

 and convex on the interior margin ; the latter is ciliated and laps 

 over the corresponding margin of the opposite gnathopod. The 

 whole forms a squamiform and efficient operculum to the organs 

 of the mouth. 



