﻿schuchert] siluric and devonic cystidea 237 



able extending from one-half to two-thirds the thecal length. The 

 ambulacrum nearest the anal region is always somewhat shorter. 

 Number of brachioles on one side of each ambulacrum varying with 

 age, there being- in the youngest known specimen 1 no. 1 ) about 5. in 

 a mature individual (no. 3 ) about [9, and in the largest example ( no. 

 4) about 22. Ambulacral grooves narrow in comparison with the 

 large size of the ambulacrals, and covered by very small rectangular 

 ambulacralia which arc sharply elevated into a median ridge. There 

 are usually from 10 to [2 ambulacralia to each ambulacral, but in 

 different specimens the number varies. The branches going to the 

 brachioles at the lateral ends of the plates have the ambulacralia as 

 well developed as the median series. Brachioles slender, composed 

 of rather large, elongate, smooth pieces. Those at the distal ends 

 of the ambulacra have 6 pieces in a column 4 mm. long; seemingly 

 these brachioles did not exceed 12 mm. in length. 



Anal area small, not prominent, and composed of 2 circles of plates. 

 The outer circle has from 7 to 9 pieces of unequal size, and the ilat 

 pyramid has 7 or 8 equal triangular pieces. 



The madreporite is rather large for Pseudocrinites, but the hydro- 

 pore is minute, and both are placed within a distinct hollow separating 

 the ambulacra of one side. 



Basal pectinirhomb smallest, that of plates 14 and 15 largest. 



Column slender, tapering rapidly for a short distance from the 

 theca, and composed of pieces of equal thickness. Length unknown. 



Comparisons. — This splendid large and odd Pseudocrinites is 

 readily distinguished from all other species of the genus by the short, 

 high, and angulated ambulacra. The form of the theca and the plate 

 sculpturing are also characteristic. 



Formation and locality. — Of this form the National Museum has 

 five excellent examples, the Geological Survey of Maryland one, Mr. 

 Gordon one, and Air. Hartley twelve. All are from the cystid beds 

 of the Manlius in the quarries near Keyser, West Virginia. The 

 specific name is given in recognition of the assistance rendered the 

 writer by Mr. George M. Perdew of Cumberland, Maryland. 



Cat. number 35,072, U. S. N. M. 



Trimcrocystis n. gen. 1 

 Generic characters. — Staurocystinae having the general structure 

 of Pseudocrinites, but differing in having 3 ambulacra instead of 2; 

 these are as long as the theca, and are R I, R IV, and R V. Another 

 ^he generic name lias reference to the tripartite divisions of the ambu- 

 lacra in this cystid. 



