Boone, Crustacea, Cruises of "Eagle" and "Ara," 1921-28 201 



Subfamily: Rhizopinae IVIiers. 

 Genus: chasmocarcinus Rathbun. 

 Chasmocarcinus latipes Kathbun. 



Plate 68, figs. A and B, 



Diagnostic characters : This is the only species of the genus so far 

 described from the West Coast of America. The carapace is box-like, 

 longitudinally convex, widest anteriorly. The eyes are directed 

 obliquely forward when seen in a dorsal view. The meral joint of the 

 ambulatories is wide. 



Type: The female holotype comes from Magdalena Bay, Lower 

 California, depth 51 fms., and is deposited in the United States Na- 

 tional Museum. 



Distribution : Hitherto known only from the holotype. The south- 

 ern range of the species is substantially extended to Cocos Island, by 

 the '^Ara" material and male specimens are for the first time recorded. 



Material examined: Three females, two males, taken inshore. 

 Wafer Bay, Cocos Island, Pacific Ocean, March 30, 1926, by the 

 *'Ara," William K. Vanderbilt, commanding. 



Technical description : Carapace box-like, longitudinally convex, 

 widest posteriorly, lateral margins converging anteriorly; frontal 

 margin relatively straight, equal to about two-fifths the frontal width, 

 superior orbital margin deeply concave, directed obliquely forward 

 and outward; the eye not quite filling the orbit; the anterolateral 

 angle is rounded; the lateral walls are high and the lateral margins 

 defined by a line which is granulate, as is also the posterior part of 

 the carapace; the anterior region is covered by punctae. A pair of 

 unusually deep longitudinal depressions, one on each side of the uro- 

 cardiac region, separate it from the branchial region; the urocardiac 

 line is clearly defined and posterior to the cardiac region is a deep 

 little pit behind the longitudinal depression. There is a fine, sparse 

 pilosity on the upper surface of the carapace which is much longer 

 on the lateral walls and legs. The sternal plastron is wide in both 

 sexes, its sutures sharply defined. The female belt is seven-segmented, 

 oval, attaining its greater width in the fourth segment; the lateral 

 margins of the second to sixth segments, inclusive, are broadly 



