MONOGRAPH OF THE EXISTING CEINOIDS. 211 



The ventrolateral edges of the pinnule segments are less frequently produced 

 than are those of the earlier brachials. Such production, resembling that of the 

 elements of the division series and of the first brachial pairs in Stephanometra, 

 is found in G olohometra and in C omatula, while in Comissia the distal ventral 

 angle of the pinniilars is produced into a long sharp spine, most marked in 0. 

 feregrina. In a few cases the dorsal outer border of the outer pinnulars may 

 be more or less extravagantly produced, standing up high above the general 

 distal profile of the pinnule. This is characteristic of the Comactiniinse, especially 

 of the genus Comactinia, and is equally well marked in some of the Comasterinse, 

 most noticeably in Comaster helli. In the genus Nemaster of the Capillasterinse 

 it also occurs, but is confined to the oral pinnules, not extending for a greater or 

 lesser distance along the genital pinnules as in the other forms. 



Occasionally only the first two pinnule segments are modified. In certain 

 species of the genera Nenmster, Comatella (fig. 1041. pi. 12), Comatxila^ and Lepto- 

 nevioster, and in all the species of the Calometridse, the two basal pinnule seg- 

 ments bear a high, thin, rounded, dorsal keel. This modification is usually con- 

 fined to the lower genital pinnules, not occurring, or being but slightly evident, 

 upon the oral pinnules; in Leptonemaster and in the species of Calometridse, 

 however, it is most noticeable on Pj, rapidly diminishing in intensity distally. 



In most of the species of Himerometridse, Mariametridse, Stephanometridse, 

 Zygometridse, and Colobometridae the segments of the lower pinnules following 

 the first two are more or less, sometimes very, strongly carinate. 



All of the species of the Oligophreata exhibit more or less tendency toward 

 a styliform or prismatic shape in their pinnules which is occasionally reflected in 

 their cirri. This is seen in the rhombic section of the cirri in Pectinoinetra acan- 

 thaster, and in the rounded triangular section of the cirri in certain of the Colobo- 

 metridfe; in Pterometra (fig. 208, p. 146) the central profile of the cirri has become 

 more or less sharpened, in the mid-ventral line being produced into a long, sharp, 

 ventral spine. 



In the pinnules whenever the tendency toward a prismatic condition is very 

 strong any production of the dorsal distal edge becomes localized and shows itself 

 at the ventrolateral angles and in the mid-dorsal line. This is best shown in 

 the lower pinnules of such species as Oligometra serripinna (fig. 315, p. 227) or 

 O. carpenten, and in E eterometra crenulata and n. producta; in a somewhat dif- 

 ferent aspect it is e\adenced in the terminal combs of the species of Comasteridse. 

 It is traceable in most of the Oligophreata. 



Next in frequency to the production of the free edges of the ossicles comes 

 the development of fine spines over more or less of the dorsal surface. There are 

 two distinct varieties of this type of ornamentation. 



When developed beyond the fir.st brachial pair the projection of the distal 

 edge of the brachials and the spinosity of the dorsal surface appear to have a 

 certain connection, for the development of a spinous dorsal surface always begins 

 at the distal edge of the segments and slowly spreads proximally. In a few species, 

 as in C osmiometra aster (fig. 215, p. 159) and in some species of Oceanometra (figs. 



