352 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.39. 



only once and curved just enough to fit closely along the posterior 

 margin of the basal joint. These maxillipeds about evenly divide 

 the space between the other mouth-parts and the first swimming legs, 

 and thus cause the mouth-parts to appear farther back than in the 

 female. But with the exception of the maxillipeds they are really 

 in the same position. 



ARTIFICIAL KEY TO THE GENERA. 



a. Second segment forming a narrow neck between the cephalothorax and the remain- 

 der of the segments, which are fused into a body incapable of flexion; all the 

 swimming legs very rudimentary; abdomen invisible. 



Tucca Kroyer, 1863, p. 352. 

 a. Third and fourth segments fused, the latter invisible in dorsal view, being cov- 

 ered by the overlapping third segment; endopods of first and second legs with 



wide and flattened joints Artacolax Wilson, 1908, p. 360. 



a. All the thorax segments except the first free and distinct; endopods of all the swim- 

 ming legs with narrow joints like the exopods b. 



h. Basal joints of first antennse enlarged, flattened, and densely bristled; sec- 

 ond maxillipeds armed with large plumose setae. 



Bomolochus Nordmann, 1832, p. 365. 



b. Basal joints of first antennae cylindrical, not enlarged, and with only a few 



setae; second maxillipeds without setae Pseudoeucanthus Brian, 1905, p. 380. 



Genus TUCCA Kroyer. 



Female. — Body with three regions, a small cephalothorax joined 

 by a short neck to a fused and inflated thoracic trunk, and a minute 

 posterior portion consisting of the genital segment and abdomen. 

 Cephalothorax inflated dorsally, with a lobed wing on either side; its 

 ventral surface deeply hollowed, with a raised rim composed of the 

 first antennse, first swimming legs and the border of the wing on 

 either side. Second antennae and mouth-parts at the bottom of this 

 bowl-shaped depression and so similar to those of Bomolochus as to 

 indicate close relationship. Maxillipeds behind and a little outside 

 the other mouth-parts, much enlarged, with powerful terminal claws. 

 First swimming legs with wide rami like those of Bomolochus; second 

 pair close behind the first, each ramus two-jointed; third and fourth 

 pairs at a considerable distance on the trunk, each with a one-jointed 

 endopod; fifth pair at the junction of the trunk and posterior body. 

 Genital segment small and triangular; abdomen rudimentary, one- 

 jointed; egg-cases cylindrical, as long as the body; eggs multiseriate, 

 small, and numerous. 



Male. — Similar to the female but considerably smaller, with the 

 same body regions, but with the genital segment larger and armed 

 with a powerful hook on either side at the posterior corner. Append- 

 ages similar with the usual sexual differences in the antennse and 

 maxillipeds. 



(Tucca, a friend of Horace and Virgil.) 



Type-species. — Tucca impressus Kroyer. 



