ISOMETRINAE 



189 



which are yellow, and the others which are white. In two specimens the four or five 

 most distal segments of some cirri are a deep brown. 



i 



Fig. 18. Isometra hordea. a, cirrus, X4. b, centrodorsal and proximal parts of rays, X7. c, brachials of 

 third syzygial pair and beyond, x 13. d, thirty-first to forty-fifth brachials, x 11. e, sixtieth to seventieth 

 brachials, x 11. /, Pj, x 11. g, a middle genital pinnule of a male, x8. /;, a middle genital pinnule of a 

 female, x 8. /', ambulacral skeleton of distal pinnules, x 60. 



Smaller cirri, whether of large or of small specimens, resemble the above, but there 

 are fewer segments longer than broad and the dorsal keel begins sooner. 



The radials are short even in young specimens; they are very short in the older. 

 (Fig. 18 A is of a specimen of medium size having complete arms of about go brachials 

 which are 58 mm. long.) They are wider distally than proximally and have concave 



