MONOGRAPH OF THE EXISTING CBINOIDS. 249 



to it, which overlaps it slightly. The outer surface of the side plates is not 

 all in the same plane. The basal portion adjoining the pinnular, which is nar- 

 rowly oval with broadly rounded ends and in maximum width about equal to the 

 distal proximal extension, is turned inward toward the pinnular; but, while all 

 of the basal portion lies in the same longitudinal plane, the two outer extensions 

 are directed slightly inward, each making a small angle with the longitudinal 

 plane of the basal portion so as to considerably increase the size of the apertures 

 through which the sacculi protrude. In some cases, where the basal portion is 

 unusually large, the lower portion is bent inward abruptly and lies on the inner 

 side of the pinnular. On the outer border of the plate in the deep, rounded notch 

 between the narrow distal and broad proximal extensions lies a small but con- 

 spicuous oval plate which almost completely fills the concavity. On the inner 

 surface of each side plate are two prominent and usually high ridges. One of 

 these, the smaller, runs along the under side of the narrow distal process to its base 

 and then, decreasing in height, curves downward and rims perpendicularly to the 

 proximal edge of the plate; frequently this ridge is not developed beyond the base 

 of the distal process. The other, much higher, runs perpendicularly outward from 

 the base, gradually decreasing in height, just touching the deepest portion of the 

 proximal excavation and traversing the outer proximal extension. 



The covering plates, which are very large and conspicuous, very fine in 

 texture with finished edges, are almost circular, slightly flattened at the base 

 where they adjoin the side plates. They lie on the outer side of the broad proximal 

 extension of the side plates and are attached by means of a ligamentous articu- 

 lation to the end of the long and straight ridge just described. 



The perisome over the genital glands is completely inclosed by large filmy 

 plates. 



In addition to the plates described, the ventral perisome on the sides of the 

 ambulacral groove contains occasional rather large multiradiate spicules, which 

 for the most part look like spiny balls. 



There are no spicules in the tentacles. 



Neometra acanthaster. The perisomic plates resemble those of N. al-ecto. 



Neometra conaminis (fig. 838, p. 405). The perisomic plates do not differ 

 essentially from those of N. alecto. 



Neometra gorgonia (figs. 839-842, p. 405). The conditions are the same as in 

 N. alecto. 



Calometra callista. There is no tangible difference between the perisome plates 

 of this species and those of Neometra alecto. 



Calometra discoidea. The perisomic plates resemble those of Neonwtra alecto. 



Gephyrometra propingua. The conditions in this species resemble those in 

 Neometra alecto, but the small plate in the notch between the distal process and 

 the broad proximal process is much reduced, being very minute, or in the form 

 of an elongate spicule parallel with the pinnulars. 



Pectinometra carduum. The conditions in this form are essentially as in Neo- 

 metra alecto; the narrow distal process is more slender and curves outward toward 



