716 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxi. 



the middle one {m) is the dividing- line between the head and the tirst 

 thorax segment, while the posterior one (/>) separates the first from 

 the second thorax segments. There is no visible groove here between 

 the second and third thorax segments, but in Trebius (Plate XV, figs. 

 1 and 2) we find that it joins the posterior sinuses of the carapace and 

 is approximately parallel with the other transverse grooves. 



The middle groove is extended outward and backward across the 

 lateral area on either side to the edge of the carapace, whei'e it makes 

 a notch similar to that left by the corresponding groove in Ti'ehJus. 

 In the three species of this latter genus it can be seen that the por- 

 tion of the lateral grooves which lies behind the crossbar of the "//"' 

 is really a part of that crossbar groove in that it completes the separa- 

 tion of the second thorax segment from the first. We are thus 

 enabled to see distinctl}^ that the anterior and outer portion of the 

 lateral areas (P, 1) is really a sort of lateral lobe or process belonging 

 to the head. The remainder of the lateral areas is similarly seen to 

 be a process or lobe (/^, ^) of the first thorax segment. In like man- 

 ner that portion of each posterior lobe of the carapace which is 

 inside of the longitudinal groove (P. 3) represents a lateral process or 

 lobe of the second thorax segment. Neither the third nor the fourth 

 thorax segments have any lateral processes. 



Like the original specimens of (itlantJcns the single representative 

 of this species was taken while swinmiing freely at the surface during 

 the \'oyage of the United States Bureau of Fisheries steamer Alhatross 

 in 18ST-8S. It is Cat. No. 327:iS. U.S.N.M. This genus Dysgaimis 

 was placed by the author among the Caligintv in a key g'iven in a pre- 

 vious paper. "^ That, however, was before the present specimen had 

 been obtained and studied. The genus evidently belongs with the 

 Euryphorina^ where it was placed by (jerstaecker, as is shown by the 

 descri})tion and figures hei'e given, but we must have a description of 

 the female before this matter can be finally settled. 



Genus DISSONUS Wilson. 



Generic diagnosis. — Only the first thorax segment fused with the 

 head to form a carapace, which is semilunar in shape and about twite 

 as wide as long. Second, third, and fourth segments free, each con- 

 siderabh' wider than long, the second one onh' provided with lateral 

 plates. Genital segment not much enlarged, without plates or proc- 

 esses, but with the entire ventral surface sparsely covered with spines. 

 Abdomen small, nearly as wide as long; anal lamina of medium size 

 and armed with large plumose setje. Egg-strings four-fifths the entire 

 length: eggs large, about 40 in each string. Antemue and mouth- 

 parts similar to those in the Caliginae and not at all like those in the 



«Proc. U. S. Nat. Mus., XXVIII, 1905, p. 533. 



