222 Bulletin, Vanderhilt Marine Museum, Yol. II 



Type: The type was obtained by the U. S. Fisheries steamer 

 ''Albatross" at Horseshoe Bend, Colorado River, and is deposited in 

 the United States National Museum. 



Distribution : Mexico — adjacent to the upper reaches of the Gulf 

 of California and south to Canos Island, Costa Rica. 



Material examined : One male and one female from Canos Island, 

 Costa Rica, February 15, 1928, taken by the ''Ara," William K. Van- 

 derhilt, commanding. 



Technical description: Carapace widest across the anterolateral 

 angles; length three-fifths of this width; decidedly convex longitudi- 

 nally ; frontal margin straight ; one-fourth of the greatest width of the 

 carapace; orbital sinus long and wide, scarcely filled by the slender 

 stalk, inferior margin visible for the greater part of its length in a 

 dorsal view, coarsely beaded ; superior orbital margin slightly sinuate 

 and margined by a flat carina, which is also continuous across the 

 frontal margin; anterolateral angles slightly peaked forward from 

 a roof above the cornea when the latter is retracted. Lateral margins 

 straight anteriorly, subparallel, then abruptly turned inward, a car- 

 inate line separating the side walls from the dorsal surface. Posterior 

 margin straight; dorsal surface glabrous, sparsely, microscopically 

 punctate. The H-shaped depression is very deep as is also the cervical 

 groove. The pterygostomian region is densely tomentose. The male 

 abdominal belt is seven-segmented, rather broad, with the tip rounded. 

 The female belt is very wide, oval, with the seven segments sharply 

 separated. 



The external maxillipeds are convex on the outer surface, close- 

 fitting into the margins of the buccal cavity, but with a distinct, 

 setae-fringed space between the two halves. The exognath extends to 

 the distal angle of the merus; the ischium is long, subrectangular, 

 with the distal margin a trifle diagonal ; the merus is scarcely half as 

 long as the ischium, squarish, with a deep median longitudinal groove 

 on its outer face, its distal margin emarginate; the palp arises from 

 the outer distal angle, its basal joint is elongate, laminate, sinuate, 

 fitting across the top of the merus; the second and third articles are 

 stocky, cylindrical, setose, as are also the inner lateral margins of the 

 merus and ischium, these setae forming a sieve-like arrangement across 

 the space between the maxillipeds. 



The eyestalk is long, slender ; the cornea terminal, large, oval, shin- 

 ing black. 



