MONOGRAPH OF THE EXISTING CRINOIDS. 



247^ 



The proximal portion of the tentacles contains a dense mass of spicules, which 

 appears as a thick roughened rod extending outward to a height equal to about 

 as much again as the height of the sacculi. 



Oligmnetra carpenten. — Each ambulacral lappet contains a very slender, 

 straight, needle-like spicule extending outward and slightly distalward in reference 

 to the pinnulars. There are no other deposits. 



There are no deposits in the tentacles. 



Oligometra serripinn-a. (fig. 780, p. 366). — Each lappet usually contains a long, 

 but extremely fine, spicule situated along the distal border aind curved in con- 

 formity with it, or straight; more rarely there are several scattered long spicules. 



At their bases the tentacles contain a few very delicat* spicules along the 

 outer side. 



In another specimen no deposits were found in the perisome of the pinnules. 



Each tentacle contained at the base two short and very narrow lines of minute 

 spicules, a distal and a proximal. 



Family TROPIOMETRID.E. 



Tropiometra vmcrodiscus (fig. 797, p. 372).— Each ambulacral lappet contains 

 a minute rudimentary plate, usually of two or three meshes, but sometimes, toward 

 the end of the pinnules, becoming of appreciable size and consisting of from 15 

 to 20 or more meshes. When this is the case the plate is more or less oval and 

 elongated in a direction perpendicular to the edge of the pinnulars, and beneath 

 it, lying between the sacculi, is another similar but smaller plate. When the cover- 

 ing plate is very rudimentary the lateral perisome of the pinnules may contain 

 very minute scattered spicules, or may be entirely naked. 



The perisome over the genital glands contains very abundant minute, rounded 

 plates and spicules which are especially numerous in parallel rows at right angles 

 to the border of the pinnulars, about one to each sacculus. 



Spicules are very few, or altogether absent, in the tentacles. 



Tropiometra afra. — Each ambulacral lappet contains a small rudimentary plate 

 of usually from two to five meshes. 



Along the sides of the pinnulars is a series of plates, usually roughly triangu- 

 lar in shape, elongated perpendicularly to the pinnulars, not quite in contact 

 basally. the distal ends of which pass between, or partially around, the sacculi. 

 There is one of these beneath each covering plate. 



There appear to be no deposits in the tentacles. 



Tropiometra carinata. — The major portion of the ambulacral lappets is usually 

 occupied by relatively large, very thin, irregular plates with rather coarse meshes 

 and irregular borders, the inner proximal comers of which are produced down- 

 ward and usually come into contact with the plates beneath. These may be reduced 

 to a single cell with radiating rods, or even to a very slender and delicate rod, 

 usually straight, sometimes irregular or forked, at right angles to the pinnulars, 

 opposite the spaces between the sacculi. 

 142140— 21— Bull. 82 18 



