of the Division Hyperina. 1 1 



tennse situated upon the inferior surface and within the anterior 

 margin; each consists of several jointsand articuli, which fold, like 

 the letter Z, upon itself. The inferior pair are long, four-jointed, 

 each joint being reflected upon the preceding." The gnathopoda 

 are complexly chelate. The first two pairs of pereiopoda are 

 long and simple; the three succeeding have the basa moderately 

 developed ; but the fifth pair are short, and in some species 

 almost rudimentary. The three posterior pairs of pleopoda have 

 the rami short, sharp, and styliform. 



On a comparison of the species of this genus with those of the 

 young animals already described, the difference will be found to 

 consist chiefly in the size of the eyes, the length of the antennae, 

 and the complexly chelate condition of the gnathopoda of Oxy- 

 cephalus. 



The young of Oxycephalies have not been observed ; yet I 

 cannot but suppose that they bear a considerable resemblance 

 to the young of the genera described, seeing that these so closely 

 approximate to the form of the adult animal. This idea appears 

 to receive sanction from observation of the young of Rhabdo- 

 soma. The only female specimens of this genus that I have had 

 the opportunity of examining carried the ova in an immature 

 state in the pouch ; but M. Guerin-Meneville has been more 

 fortunate : when he was so obliging as to show me his valuable 

 collection of Amphipoda, he drew my attention to the form of 

 the young of Rhabdosoma, which he had figured among his 

 drawings. His figure of the young of Rhabdosoma appeared to 

 me to be a fair representation of an adult Oxycephalies. With- 

 out going into the details of its structure, I think we may con- 

 clude that the young of Rhabdosoma bears a general resemblance 

 to the young of Platyscelus. Thus we may remark that the 

 young of Vibilia, Brachyscelus, Leptoscelus, and Rhabdosoma — 

 animals, in their adult condition, very unlike each other — bear 

 a considerable resemblance to one another in their young state. 



In speaking of the morphology of this group, it must not be 

 confounded with that of the Decapod forms, where the young 

 animal leaves the egg and the care of the parent in an embryonic 

 condition, and where the organs that are obsolete or secondary 

 in the adult are made subservient to the uses of the animal in its 

 immature condition. The morphology of the Brachyura is due 

 to the development of parts that in the early condition of the 

 animal are not visible. The creature, starting upon its errand of 

 life at too early a period for the true limbs to have been moulded 

 to their useful form, makes use of others that can only be avail- 

 able to an animal in an immature or degraded state. 



In the Amphipoda the young quit the egg with the perma- 



