AMPHIPODA, 219 



DlCTYLOCETlA, Lat. 



The body not thickened anteriorly; tlie head moderate, depressed, 

 nearly square ; eyes small ; four extremely short antennae composed 

 of but few joints, as in Phrosine, of various forms — the inferior being 

 thin and styliform, and the superior terminated by a small concave 

 plate on the inner side — resemble a spoon or forceps *. 



The others — GAMMARiNiE, Latr. — always have four antennae ; their 

 body, invested with coriaceous and elastic segments, is generally 

 compressed and arcuated ; the posterior extremity of the tail is de- 

 prived of fins; its appendages are styliform and cylindrical, or conical. 

 At least two of their four anterior feet are usually terminated by a 

 forceps. 



The vesicular bursse, 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 inclose the ova are six in number. 



Sometimes the four antennte, although of different proportions in 

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

 blance to feet nor do they perform their functions. 



A subgenus which we have established under the denomination of 



loNE, Lat., 



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

 cicus, Ti'ans. Lin. Soc, IX, IH, 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 antennaj 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 Avhole inferior surface of the body, 

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

 cealed 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 l)y means of his forceps. It is a rare animal 

 which, in its habits, approaches the Bojjyri f. 



All the ensuing Amphipoda have the segments of the body perfectly 

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



* Phros. seminulafa, Risso, lb. ; Desmar. The stem of the inferior antennae consists of 

 two Of three joints, while in Piaosine it is inarticulate. There also, the joints of the 

 peduncles of the same antennaj are shorter. 



t See Ann. des iSc. Nat., Decemb. 1826, XLIX. 10, the male — 11, the female. 



