MONOGRAPH OF THE EXISTING CKINOIDS. 



279 



and sizes of the cirrals. A similar conservatism is displayed by the penultimate 

 segment, tliis being much less variable than the preceding segments, though not so 

 constant as the terminal claw. The penultimate segment is in effect an interme- 

 diate between the terminal claw and the cirrals preceding it. 



In structure the penultimate segment resembles the preceding cirrals, being 

 devoid of the vitreous cortical layer covermg the terminal claw. Except in rare 

 cases where the terminal claw is reduced to a straightened, blunted, and shortened 

 conical finial appendage, the penultimate segment almost always bears, at least in 



Fig. 324. 



x:53xm:xxiizn] 



Fig. 325. 



X — r~nD 



Figs. 324-326.-324, A CIEKnS FBOM a specimen of NEMASTEE INS0UTU3 FEOM BASBADOS viewed (a) DOKSALLT AND (6) LATER 

 ALLY. 323, .\ CIRRUS FROM A SPECIMEN OF LEPTONEMASTER VENCSTC3 FROM THE WEST COAST OF FLORIDA \1EWED (a) 

 DORSALLT AND (6) LATERALLY. 326, A CIRRUS FROM A SPECIMEN OF CoMATHJA IRIDOM ETRIFORMIS FROM THE SOUTHEASTERII 



United States viewed (a) dorsally and (6) laterally. 



the majority of the cirri in a given individual, a more or less, sometimes quite, erect, 

 sharp dorsal spine, known from its relation to the terminal claw as the opposing 

 spine which, with the latter, forms a more or less chelate tip to the cirrus (figs. 4, 

 p. 63, and 314, 31.5, 317, 318, p. 273); but the similarity to the crustacean or 

 arachnid chela is somewhat lessened by the fact that the terminal claw is almost 

 immovably articulated to the penultimate segment. 



The opposmg spme (fig. 4, j). 63) differe somewhat phylogenetically and 

 ontogenetic ally from the dorsal spines on the preceding segments, being closer to 



