90 CRUSTACEA. 



cal. At least two of their four anterior feet are usually terminated 

 by a forceps. 



The vesicular bursae, in those where they have been observed 

 the Gammarinae,Latr. are situated at the exterior base of the feet, 

 commencing with the second pair, and are accompanied by a small 

 plate. The pectoral scales which enclose the ova are six in number. 



Sometimes the four antennae, although of different proportions in 

 several, have a similar form and uses; the inferior have no resem- 

 blance to feet nor do they perform their functions. 



A subgenus which we have established under the denomination of 



Ione, Lat., 



Only, however, from a figure given by Montagu Oniscus thora- 

 cicus, Trans. Lin. Soc. ,IX, III, 3, 4 exhibits very peculiar charac- 

 ters which separate it from all others of the same order. The body 

 consists of about fifteen joints, but only distinguished by lateral 

 tooth-like incisions. The four antennas are very short; those that 

 are external, being longer than the others, are the only ones visible 

 when the animal is seen on its back. Each of the two first segments 

 of the body of the female is provided with two elongated, fleshy, 

 flattened cirri resembling oars. The feet are very short, concealed 

 under the body and hooked. The six last segments are furnished 

 with lateral, fleshy, elongated, fasciculated appendages, which are 

 simple in the male and like oars in the female. At the posterior 

 extremity of the body we also observe six simple, recurved appen- 

 dages, two of which are larger than the others. The abdominal 

 valves are very large, cover the whole inferior surface of the body, 

 and form a sort of receptacle for the ova. This animal remains 

 concealed under the shell of the Calinassa subterranea, on the side 

 of which it forms a tumour. Montagu, having withdrawn one of 

 these Crustacea from its domicil, kept it alive for several days. The 

 female is always accompanied by the male, who fixes himself firmly 

 to her abdominal appendages by means of his forceps. It is a rare 

 animal which, in its habits, approaches the Bopyri(l). 



All the ensuing Amphipoda have the segments of the body per- 

 fectly distinct, throughout their whole extent; in neither sex nor in 

 any of the species do we find those long oar-like cirri observed in 

 the first of the Iones. 





(1) See Ann. des Sc. Nat., Decemb. 1826, XLIX, 10, the male II, the fe- 

 male. 



