354 PROCEEDINGS OF THE NATIONAL IIUSEUM. vouxxxin. 



They wished to inchide in the same genus Dana's Lepidopus, and the 

 above diagnosis was evidently made out with that in view. 



And they also gave two species diagnosis, one for their new species 

 dentatus, and the other for Dana's species armatus. 



But in this they were mistaken, for Dana's genus Lepidopus can 

 not be identified with Perissopus for reasons already mentioned (see 

 p. 848). This leaves the genus with the original type species dentatus, 

 the new species, communis, established by Rathbun in 1887, and a 

 third species, incisus, described in 1892. 



In that year Van Beneden published an account of a copepod para- 

 site belonging to the present subfamily, which he made the type of a 

 new genus, called Ohlamys. He recognized its resemblance to Dana's 

 Lepidopus, but was either unacquainted with, or had forgotten 

 Steenstrup and Liitken's genus Perissopus, which it resembles even 

 more closely. In fact there is little doubt that it is a species of Peris- 

 sopus, as Bassett-Smith has suggested (1899, p. 468), and as such it 

 is here included in the key. The only doubt as to its identity is found 

 in the utter confusion of details characteristic of Beneden's figures and 

 descriptions. In his ventral view of the female (Plate II, fig. 3) he 

 pictures the first swimming legs as uniramose and two-jointed, while 

 the other three pairs are biramose, with all the rami one-jointed. In 

 the enlarged figure (fig. 9) of these same legs he shows them all bira- 

 mose, each endopod one-jointed, and each exopod two-jointed. His 

 description in the text (pp. 230 and 231) agrees with this last figure, 

 except for the fourth legs, of which he says: "La quatrieme paire de 

 pattes n'est pas biramee." In the face of such flat contradictions, 

 one has to be guided chiefly by the general makeup of the body and 

 the relation of its regions. These are so similar to those of Perissopus 

 as to leave no doubt of generic identity. 



PERISSOPUS COMMUNIS Rathbun. 



Plates XVII and XVIII. 



Perissopus communis Rathbun, 1887, p. 560, pis. xxix, xxx. 

 Perissopus dentahcs (part) Bassett-Smith, 1899, p. 468. 



Female. — Carapace semielliptical, narrowed but little anteriorly, 

 widest at or near the posterior angles ; lateral margins slightly convex, 

 sometimes nearly straight; posterior lobes short and angular; poste- 

 rior margin straight or slightly concave, sometimes wdth a small spine 

 on either side. Frontal plates narrow but distinct, frontal margin 

 nearly straight, with a broad and shallow median incision. Eyes 

 usually invisible in the adult, but distinct in the young, three in num- 

 ber and arranged in a transverse row, the central one slightly behind 

 and a little smaller than the other two. Visible portion of the dorsal 

 plates of the second thorax segment standing out at an angle of 45° 

 to the central axis, and elliptical in outline, the longer diameter nearly 



