37 



337 



the ischiuin-merus broad, oblong, longitudinal in position, the two segments subequal 

 and subquadrate, fused, but with a faint suture line visible; palpus small, articu- 

 lated on the anterior margin and near the outer angle of the merus, the three seg- 

 ments end to end; exognath exposed. 



DilTers from other genera of Pinnotheridce in the longitudinal direction of the 

 maxillipeds, combined with the small palpus. The exognath is of important size 

 as in the subfamily Asthenognathinœ. 



Type and only species : 



Mortensenella forceps Rathbun. 



Plate I, fig. 18. 

 Mortensenella forceps Rathbun, Proc. Biol. Soc. Washington, XXII, 111. 1909. 



Carapace 15 times as wide as long, lateral angles rounded; surface punctate 

 and pubescent, a transverse groove through the middle. Fronto-orbital distance 4 

 as great as width of carapace, edge of front straight in dorsal view, sides oblique, 

 a median furrow. Upper margin of orbit rounding into the side margin of the 

 carapace, which margin is emphasized by a sharp raised line cut into crenulations 

 by closed fissures. Posterior margin straight, equalling the length of the carapace; 

 a fine sharp ridge just above and parallel to the margin. Orbits oblong, lower 

 margin ill-defined. Epistome deep in the middle, bilobing the anterior margin of 

 the buccal cavity. Both the anterior angles of the merus of the maxillipeds are 

 rounded off; exognath about one-third as wide as endognath , provided with a 

 slender palpus. 



Clielipeds of male equal, smooth and 

 punctate. Inner margin of wrist rounded. Palm 

 well-developed, suboblong; fingers strongly 

 curved away from each other, making a wide 

 gape into which a large truncate tooth pro- 

 jects from the dactylus; extremities of fingers 

 horizontal, very slender, sharp, tips horny. In 

 the single female collected, only one cheliped 

 is present; it is much smaller than in the 

 male but similar, the horizontal extremities 

 being proportionally longer. 



First three legs similar, first and third of subequal length, second longer, about 

 2'5 times length of carapace. Fourth leg much reduced in length and width, reach- 

 ing little beyond the merus of the third. Legs and also the arm,; with granulated 

 margins; dactyli elongate. 



Sternum of male coarsely punctate ; margin of abdominal cavity finely beaded. 

 Abdomen of male narrow-triangular, with a constriction at middle of fifth segment, 

 terminal segment oblong; the appendages of the first segment would exceed the 

 abdomen if extended, but they are bent sharply backward opposite the posterior 



Fig. 21. Mortensenella forceps, c? cotj'pe. 



7 ram. wide: a, abdomen; b, abdominal 



appendages; c, chela; d, maxilliped. 



