THE CANCROID CRABS OF AMERICA 31 



First article of antennules very broad. Buccal cavity rounded 

 anteriorly. The endostome has a strong crest defining the respira- 

 tory canal. Merus of outer maxillipeds subquadrate and slightly 

 truncate at its inner angle for insertion of palp. Chelipeds short. 

 Ambulatory dactyls slightly widened; those of last pair shorter and 

 more compressed than the preceding, their penult article elongate. 

 Contains only one species. 



COENOPHTHALMUS TRIDENTATUS A. Milne Edwards 



Plates 11 and 12; Plate 13, Figures 3-5 



Coenophthalmus tridentatus A. Miln'e Edwards, Crust. Reg. Mex., 1879, p. 237, 

 pi. 42, figs. 2-26 {Ctenophthalmus on explanation of plate) (type-locality, 

 Montevideo; figured type in Paris Mus.).^ 



Diagnosis. — Subquadrilateral. Three lateral teeth. Front arcu- 

 ate. Legs spinuous. 



Description. — Carapace broader than long; surface uneven and 

 rugose with numerous short transverse lines on which very short 

 hairs are inserted. Front very wide, arcuate, subentire, or slightly 

 wavy and obscurely four lobed; a slight sinus separates it from the 

 inner orbital angles which are shallow rounded lobes. Orbital bordel 

 deeply cut and v/ith two small open fissures above and a large 

 V-shaped outer emargination. Eye short and thick. Antero-lateral 

 border three-toothed; first tooth at outer angle of orbit shallow, with 

 a minute point; the others tipped with a slender spine, the third nar- 

 rower than the second. Postero-lateral borders nearly twice as long 

 as antero-lateral, thick and slightly convergent. Posterior border 

 very wide. Pterygostomian region, sternum and legs covered with a 

 short velvet like that on dorsal surface of carapace. 



Chelipeds stout. The arm overreaches the carapace very little; it 

 has three spines on its inner margin, four on its upper. Carpus with 

 a strong acuminate inner spine, and various spinules on the upper- 

 outer surface. Palm with a double denticulate crest above, outer 

 surface rugose. Fingers short, channeled, prehensile borders sharp, 

 cut into several close-set teeth. Merus of first three ambulatory 

 legs spinous above; the last leg has two or three spines below on 

 the distal half; the propodus of each leg has a pair of spines at distal 

 end below, one spine outside, the other inside. Abdomen of male tri- 

 angular from the fourth segment to the tip; a naked, transverse 

 swelling on each segment from the second to the sixth inclusive. 



Measurements. — Male (15406, B. A. Mus.), length of carapace 11, 

 width of same at last tooth 15.6, fronto-orbital width 11.8, mdth 

 between orbits 7.9 mm. In the specimens examined the females run 

 larger than the males: Female (Mar del Plata), length of carapace 



' The figured type is said to be female in explanation of plate (probably correct), but male in text, p. 238 . 



