MONOGRAPH OF THE EXISTING CBINOIDS. 



153 



p. 213, and 285, p. 215) also the genital pinnules are more or less longer than the 

 distal. In the Thalassometrinfe and Charitometridse, and in highly multibrachiate 

 types, the genital and distal pinnules are usually of approximately the same length. 



In a single comatulid. Isometra vivipara, the genital pinnules of the female 

 differ from those of the male. In those of the female (fig. 1238, 1240, pi. 38) the third 

 and fourth segments are enormously widened, chiefly on the distal side, to cover 

 the brood chamber. On the proximal portion of the arm the fifth segment also is 

 slightly widened. Toward 

 the end of the series of 

 genital pinnules the broad- 

 ening of the segments dimin- 

 ishes, first the fifth, then 

 the fourth segment assuming 

 the normal form, the third 

 only remaining broad. A cor- 

 responding development takes 

 place in the growing young, 

 small specimens having only 

 the third segment of the 

 lowest genital pinnules wid- 

 ened, while the outer genital 

 pinnules show no widening 

 of any of their segments. 



The male genital pin- 

 nules (fig. 1239, pi. 38) 

 also broadened, though not so 

 much as the female. Here 

 the broadening begins on the 

 third segment, which is the 

 widest, and continues, grad- 



212 



ually diminishing, to about 

 the middle of the pinnule. 

 It is developed to about the 

 same degree on both the 

 proximal and distal sides. 



Hie segments OI the gem- J,IJ G 212. LATERAL VIEW OK SPECIMEN OF ] IAIIJALOMEI I-A HANA. 



tal pinnules, except for those 



which are broadened, are fairly slender and smooth, the distal having only a slight 



development of spines on their distal borders. The articulations are not swollen. 



The number of segments in the genital pinnules varies from 5 or 6 to about 

 25 ; the usual number is between 10 and 15. 



The gradual transformation of the genital into the distal pinnules is not 

 distributed uniformly among the segments of succeeding pinnules. It commences 

 at the distal end and gradually extends downward toward the base, after the 



