ISOPODS OP NORTH AMERICA. 



601 



do not differ from specimens of Oniscus aselhis in the U. S. National 

 Museum collection. 



Body oblong-ovate, about one and a half times longer than wide, 10 

 mm. : 16 mm. 



Head wider than long, 2 mm. : 3 mm., with the frontal margin 

 slightly convex and pronounced antero-lateral lobes, narrow and elon- 

 gated, almost 1 mm. in length and rounded anteriorly. The eyes are 



FIG. 657. ONISCUS ASELLUS (AFTER SARS). a, MANDIBLE, b, POSTERIOR LIP. c, ANTERIOR LIP. 

 d, SECOND ANTENNA, e, FIRST ANTENNA. /, SECOND MAXILLA, g, FIRST MAXILLA, h, MANDIBLES. 

 i, DORSAL VIEW OF BODY, j, MAXILLIPEDS. k, HEAD (LATERAL VIEW). I, FIRST PLEOPODS OF 

 MALE. TO, HEAD (VENTRAL VIEW), n, FIRST PLEOPODS OF FEMALE, o, SECOND PLEOPOD OF MALE. 

 p, UROPOD. q, ABDOMEN (VENTRAL VIEW), r, LAST SEGMENT OF ABDOMEN, s, SEVENTH LEG. 

 t, FIRST LEG. M, THIRD PLEOPOD OF FEMALE. 



small, composite, and situated at the sides of the head, at the base of 

 the antero-lateral lobes. The first pair of antennae are small and incon- 

 spicuous and are composed of two articles. The second antennae have 

 the basal article short; the second article is twice as long as the first; 

 the third is equal in length to the second; the fourth is nearly twice as 

 long as the third; the fifth is one and a half times as long as the fourth. 



