620 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Table 15.— Details of some specimens o/ Isometra in the British Museum collection 



[See also Table 16, for I. vivipara, on p. 635.] 



KEY TO THE SPECIES OF ISOMETRA 



[by A.M.C.] 

 a'. Pj similar to, or larger than, Pi. 



bK The first genital pinnule is Pj or P,; P, and Pj (when not genital) each with 5 or 6 segments and 

 about 2 mm. long, P, slightly smaller (only known from off Uruguay; 1097 meters). 



angustipinna (p. 621) 

 V. The first genital pinnule is P, or Pj; P, and Pj each with 8 or more segments. 



c'. Cirri XL-LXII, 25-75; in the female the third to seventh segments of the genital pinnules 

 are expanded; a very robust species, most of the specimens taken having the length IBr, 

 to Brj (inclusive) from 11-16 mm. (from Clarence Island and the South Shetland area; 

 117-490+ meters) hordea (p. 622) 



