56 BULLETIN 54, UNITED STATES NATIONAL MUSEUM. 



they terminate in a strong hook. Head of adult male armed with 

 powerful forward-projecting curved jaws or mandibles. First seg- 

 ment of thorax is united with the head, but separated by a suture line. 

 Seventh thoracic segment small, resembling those of abdomen. Abdo- 

 men abruptly narrower than thorax and composed of six segments. 

 Mandibles wanting in female. No true incubatory pouch present. 

 Oral parts in female reduced to maxillipeds only; in male to mandibles 

 and maxillipeds. Sexes very different in appearance. Body of male 

 depressed and dilated in front; that of female more or less fusiform. 

 Larval form also different, but resembling female. 



12. Genus GNATHIA Leach. 



Head of male large, subquadrangular. Head of female rather 

 small, subtriangular. Thorax composed of five well -developed seg- 

 ments, the other two segments being rudimentary, the first being 

 fused with the head and the seventh placed between the project- 

 ing lateral parts of the fifth segment. First pair of legs in male 

 operculiform, composed of two articles; those of female subpediform, 

 being divided into three or four articles. There are five pairs of 

 ambulatory legs. Abdomen much narrower than the thorax. Man- 

 dibles present in male, more or less flattened and projecting anteriorly 

 beyond the head. Maxillipeds without epignath; palp composed of 

 four articles. 



ANALYTICAL KEY TO THE SPECIES OF THE GENUS GNATHIA. 



a. Mandibles in male with the basal part ornamented on the superior margin with 

 an elevated crest, which is irregularly dentate. Legs furnished with many 



spiny processes ' Gnathia criMata ( Hansen) 



a' . Mandibles in male without elevated crest on the superior margin. Legs without 



spiny processes. 



b. Mandibles in male with slight notch outside, inner edge obtusely produced in 

 the middle, tip acute, slightly incurved. Front of head not produced in the 



middle beyond the antero-lateral angles Gnathia elongata (Kr0yer) 



b f . Mandibles in male carinate on outer side near the middle, the carina ending in 

 a tooth-like process, irregularly and bluntly toothed near the base within, 

 turned upward at apex. Front of head produced in the middle much beyond 

 the antero-lateral angles Gnathia cerina (Stimpson) 



GNATHIA CRISTATA (Hansen). 



Anceus cristatus HANSEN, Vidensk. Meddel. Naturh. Foren. i. Kj0bh., 1887-1888, 



p. 182, pi. vn, fig. 2-2a. 

 Gnathia cristata RICHARDSON, American Naturalist, XXXIV, 1900, p. 214; 



Proc. U. S. Nat. Mus., XXIII, 1901, p. 506. 



Locality. Latitude 72 32' north, longitude 58 51' west. 

 Depth. 116 fathoms. 



See Sars's Crustacea of Norway, II, 1899, p. 50, and Harger, Report U. S. Comm. 

 of Fish and Fisheries, 1880, Pt. 6, pp. 408-410, for characters given below. 



