NO. 1504. A MERICA N PA RASITIC COPEPODS— WILSON. 683 



The three terminal claws on the end of the exopod of the first swim- 

 ming- legs are toothed, the first one along- the posterior margin, the 

 other two along both margins. 



The genital segment shows two pairs of rudimentary legs on its 

 ventral surface, the first pair two-thirds of the length from the ante- 

 rior end and close to the lateral margins, the second pair at the 

 posterior corners. 



The semen receptacles are sausage-shaped, the posterior portion 

 enlarg-ed into a more or less spherical sac, the anterior part made up 

 of the coiled duct. 



Total length, 4.5 mm. Length of carapace, 2.3 mm. ; of genital seg- 

 ment, 0.8 mm.; of abdomen, 1.10 mm. Width of carapace, 2.8 mm.; 

 of genital segment, 0.6 mm. 



Color as in female. The United States National Museum collection 

 includes a single lot of this species, numbering eight specimens, which 

 were taken from a skate off the coast of Shetland (Cat. No. 8033, 

 U.S.N.M.), and are all finely preserved. 



This is Kroyer's original type species of the genus; he described the 

 female in 1838 and the male in 1863. 



It is a ver}' common species and has been described b}- man}' zoolo- 

 gists since Kr63"er's day, each in his turn adding something to the 

 details already known. The present account has collected all these 

 details and supplemented them where lacking, and also supplies sev- 

 eral new figures, bringing the account of the species up to date. Cer- 

 tain of the figures have been placed on Plate XV in order to facilitate 

 a comparison between the three species and thus bring out more clearl}' 

 the specific differences. The three species have been under the 

 author's observation simultaneously, and there can be no doubt of 

 their validity. 



SubfaiTiily E;i:rpj,Yr»iiORiN".gE. 



Sexes similar as in the Caligina?. Carapace broad and compressed, 

 made up of the three anterior thorax segments fused with the head. 

 The fusion, however, is not always as complete as in the Caliginee, but 

 shows a marked transition in the different genera. In Alebion and 

 Glolopotes the three first segments are fully blended with no grooves 

 between them. In Euryphorm and Dysgamus the second and third 

 segments are fused intei' se, but are well separated from the first, 

 while in the new genus Dlssonus all three thorax segments are free 

 and as completely separated as in the Pandarina?. 



Frontal plates well defined, but never furnished with lunules. The 

 fourth thoracic segment small, free, and furnished in the females with 

 a pair of dorsal plates which usually overlap the following (genital) 

 segnient. This latter is large and nearly always lobed posteriorly; it 

 is covered in Euryphonis with a large membranous wing made up of 



