CLINTON GROUP, 



179 



CKINOIDEA OF THE CLINTON GROUP. 



There are a few species of this family of fossils, peculiar to the Clinton group, or which 

 do not appear in the Niagara group. These species, with a single exception, are of types quite 

 distinct from those of the lower silurian period, and show a greater affinity with those of the 

 succeeding period. In the upper limestone of this group, several species have been observed, 

 which are identical with those of the Niagara group ; while those species in the beds beneath 

 this limestone, are quite distinct. In all the localities examined, the crinoids in this group are 

 found in a broken and dilapidated condition ; and the short intervals of quiet alternating with 

 periods of disturbance, or a change in the nature of the sediment, has operated unfavorably to 

 the growth and preservation of these animals. 



Genus CLOSTEROCRINUS {nov. gen.). 

 [Gr. xXujTTip, fiisus, and xpivov, lilium.] 



The structure, as given under specific decription below, characterizes the genus. It is the 

 earliest form known, having only three plates in the first series, as this one appears to have, 

 judging from the side exposed to view. 



572. 1. CLOSTEROCRINUS ELONGATUS («. sp.). 



PL. A XLI. Fig. 2 a-f. 



Body subfusiform, elongated, gradually tapering below and above, with ten pairs'? of arms 

 which are narrow and closely arranged ; surface nearly plain, or with fine ornament ; pelvic 

 plates three 1 which are surmounted by five in the second series ; third series of plates irregular, 

 or with intercalated plates ; arms and fingers composed of quadrangular joints, with jointed 

 tentacula ; column round, enlarging above where it joins the pelvis, composed of alternating 

 thicker and thinner joints, except in the upper part, where there are two or three thin ones to 

 one thick one. 



The only specimen known, and from which the figure and description are taken, is imperfect 

 on the exposed side, while the stone adheres to the opposite side. The structure shown in the 

 righthand figure can be clearly made out, but the subdivisions beyond tliis are too obscure to be 

 defined. This form is remarkable for the narrow deep cup, which enlarges very gradually from 

 the pelvis to the base of the arms, where it seems contracted. The column is much enlarged at 

 its junction with the pelvis. 



Fig. 2 a. The specimen, natural size. 



Fig. 2 b. The structure of the calyx enlarged, showing one side with column below. 

 Figs. 2 c, d, e,f. Portions of the columns and sections, natural size and magnified. 

 Position and locality. In the upper limestone of the Clinton group, Lockport, Niagara 

 county. (Collection of Col. Jewett.) 



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