68 COOK 



ONYCHELUS OBUSTUS sp. nov. 



Type. No. 797, U. S. Nat. Mus. Collected in the Colorado 

 desert by C. R. Orcutt. 



Length of male 38 mm., width 3.8 mm. ; female 39 mm. by 4.2 mm. 



Colors in alcohol black and dull yellow or clay-color. Segments in 

 front of posterior suture dull black to below the pores ; posterior zone 

 reddish above, the ventral surface, legs, and antennae clay-color. 



Clypeal foveolae five on each side ; some distance above the foveola 

 two oblique rows of small irregular depressions, the rows converging 

 upward. 



First segment with a very distinctly raised anterior margin extending 

 from the lateral corners to near the eyes where the limiting groove bends 

 inward and is suddenly obliterated. The edge is concave along the 

 raised margin, to accommodate the inflated angle of the head, and the 

 lateral corner is rather pointed. 



Segments nearly smooth above ; in front of the constriction they are 

 quite even, but the black surface does not shine. Behind they are ab- 

 ruptly thicker and distinctly convex ; the surface shines, though it is less 

 even, being marked by indistinct and irregular longitudinal shallow 

 grooves or depressions. The suture of the median line is marked by a 

 fine sulcus, and that behind the pore is deep and distinct. The longitud- 

 inal grooves become more distinct below the pores, and pass gradually 

 into the normal strictions more than half way down to the legs. Pleural 

 sutures distinct, but less so than the others. The surface of the anterior 

 part of each segment below is ornamented with a delicate network 

 which takes the place of the concentric striations. 



Last segment very broadly and evenly rounded, the surface inflated 

 and convex, both above and on the sides. Anal valves evenly convex, 

 polished, and shining. 



Gonapods with ventral plate and mesial corners of anterior lobes 

 much produced ; lateral lobes broadly triangular, the short apex turned 

 outward ; posterior gonapods concealed, slender, simple, falcate. 



Numerous specimens of both sexes have been examined. They are 

 entangled with numerous cactus spines, indicating an intimate associa- 

 tion with these plants. 



Order Coelocheta. 



The Coelocheta are a distinctly temperate and boreal group, and are 

 probably represented by several species in Alaska. The creatures are 

 small and unusually agile, and are poorly represented in collections. 

 This applies especially to the suborder Chordeumatoidea, many of 



