54 Bulletin American Museum of Natural History [Vol. LII 



the rest of the limb suppressed. Uropod 1, outer margin of outer ramus, and inner 

 margin of inner ramus finely serrate. Uropod 2, rami without serrations. Uropod 3, 

 outer ramus with inner edge serrate, inner ramus with outer margin and upper part of 

 inner margin serrate. Telson with edges nearly straight, slightly constricted at base. 



Length. — 5.5 mm. 



Female. — Like the male generally but with the thorax much broader propor- 

 tionately. Head with front perpendicular, and rostrum short and broad. Antenna 1, 

 first joint about as long as all the rest combined, second joint twice as long as third, 

 flagellum with three joints of about equal length but successively narrower. Antenna 

 2, fourth joint slightly shorter than fifth, fifth equal in length to the flagellum which 

 consists of one joint with a few setules near the distal end. 



Length. — 5 mm. 



Tetrathyrus sancti-josephi, new species 



Localities. — San Josef Island, Gulf of California, electric light; 1 specimen (1 

 d" type). Agua Verde Bay, Gulf of California, electric light; 1 specimen. Carmen 

 Island, southeast side, Gulf of California, electric light; 25 specimens. 



Male. — In general this species closely resembles Tetrathyrus moncoeuri Steb- 

 bing; but in a few characters it differs from that species. In the second antenna the 

 fifth joint extends only to the smallest degree beyond the fourth. Perseopod 5 

 consists of only the first and second joints; the second joint is curved, about three 

 times as long as wide, and terminates in a small knob. Uropods agreeing very closely 

 with those of T. moncoeuri except that no division can be observed between the inner 

 ramus and peduncle of uropod 2, thus forming a coalition as in uropod 3. Telson 

 without terminal spinules. 



Length.— 4 mm. 



Female. — Front of head perpendicular, not sloping at all forward as in the male. 

 Antenna 1, flagellum equal in length to the peduncular joint, first joint of flagellum 

 very short, second joint about three times as long as first and bearing a group of four 

 setae about the middle of the upper edge and one at the distal end, third joint about 

 two-thirds as long as second and bearing two short spinules about the middle of the 

 upper edge, one on the under edge near the distal end and one at distal end of upper 

 edge, fourth joint a very little more than one-half the length of the third and bearing 

 one or two minute spinules at the distal end. Gnathopods very closely resembling 

 those of male; the lower distal angle of the sixth joint is not so much produced but is 

 rather blunt and bears a single spinule. Perseopods 1-3 as in male. Perseopod 4 with 

 second joint proportionately broader and the rest of the limb proportionately shorter 

 than in male. Perseopod 5, second joint proportionately much narrower than in male 

 and tapering off distally into an acute point. In one female examined the second 

 joint of this perseopod ended less acutely and appeared to have a very minute third 

 joint or an enlarged terminal spine as shown in the figure. Telson and uropods as in 

 male except the rami end in more acute angles. Uropod 2 as in male has the inner 

 ramus united with the peduncle. 



Length. — 4.5 mm. 



