AMPHIPODA FROM COSTA IlICA-STEBBTXCr. 999 



The first maxillpe have three setse on the apex of the inner plate, 

 instead of the two whicli appear to be the usual number in this genus.' 



The lirst gnathopods have a spiniferous boss, more developed in the 

 male than in the femile, on the hind margin of the fourth and lifth 

 joints, and the palm of the subparallel-sided hand nearly transverse, 

 not overlapped by the small finger. 



In the male the large second gnathopods are very similar to those 

 of IlyaleJla dentata Smith, and Ilyalella longlstUus (Faxon), but the 

 hand is rather longer in proportion to the breadth. The palm ends in 

 a slight bulging beyond the pocket into which the apex of th<^ strongly 

 curved finger closes. Near the hinge of hand and finger the palm has 

 a somewhat tooth-like indent, just like the "notch" of 11. dentata 

 as figured and described by Prof. S. 1. Smith, the slope of the palm 

 being nearly straight and beset on each side with spines. In the 

 female the hand is as long as the wrist, considerably wider distally 

 than in tlie proximal half, the small, closely shutting finger not reach- 

 ing the end of the palm. So far as can be judged from Professor 

 Smith's complete lateral view of the female of his //. inernils, both 

 gnathopods in the female of that species are in close agreement with 

 those of the present species. 



The third pera^opods are much shorter than the fourth or fifth 

 pairs. In all three the second joint may be described as large and 

 broadly oval, l)ut in the fifth pair it is considerably broader and more 

 rounded than in the. other two pairs, with a length not much greater 

 than the breadth. No "accessory branchiae ■' were observed in con- 

 nection with any of the limbs. 



The third uropods are quite small, with the rannis taixM-inu-. nearly 

 as long as the peduncle, but much narrower. 



The telson is almost square, the distal margin carrying a ])aii- of 

 setules, its corners rounded. 



A male specimen measured from front of head to the extremity of 

 the slightly bent pleon three-tenths of an inch (7..5 mm.). 



The specimens, 20 in number, were laljeled as coming from a 

 height of 2,400 meters, or 8,000 feet, on Volcan Reventado, and 

 collected by Mr. P. Biolle3\ 



The specific name is given in compliment to Dr. "Walter Faxon, 

 who in 1876 described several species of this genus and directed 

 attention to some of the difficulties attending the delimitation of spe- 

 cies within it. Dr. Faxon at that date« writes: "After an examina- 

 tion of a large number of Ilyalella dentata and //. huiunk from 

 Utah, I am satisfied that they are but varieties of one species. The 

 form with dorsal teeth on the first and second abdominal segments is 

 very probably synonymous with Amphitoe aztecus Saussure* and 



« Bull. Mus. Harvard, III, p. 374. 



ftMemoire sur divers Crustacc^s uuiiveanx du Mexique et des Antilles, 1858, p. 58, 

 pi. v, fig. 33. 



