620 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



TABLE 15. Details of some specimens of 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 1 . P2 similar to, or larger than, PI. 



b>. The first genital pinnule is P 2 or P 3 ; PI and P 2 (when not genital) each with 5 or 6 segments and 

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



angustipinna (p. 621) 

 V. The first genital pinnule is P 4 or P 5 ; PI and P 2 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 IBri 

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

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



