INVERTEBRATES. 169 



radial pieces above the first one always well developed. The general form of 

 the eutire body in these two genera, is likewise very different. 



The proposed genus Cotyledonocrinus, Cassedy and Lyon, appears to agree 

 exactly in all respects with Dichocrinus, excepting that it has no anal piece on 

 a range with the five first radials, and in contact with the base. This feature, 

 however, as suggested by Dr. Shumard, is probably abnormal. If not, it may 

 be a good generic distinction. 



So far as known, the genus Bichocrinus was peculiar to the Carboniferous 

 epoch. 



Dichocrinus conus, M. and' "W. 



PI. 16, Fig. 5®, 55. 

 Dichocrinus conus, Meek and Worthen, Sept., I860. Proc. Acad. Nat. Sci., Pliil., p. 381. 



Body large, abconical, longer than wide, composed of rather 

 thin smooth plates, connected by close fitting linear sutures. 

 Base comparatively large, a little wider than high, tapering 

 rather rapidly to the small inferior extremity, which is trun- 

 cated, and provided with a small, slightly projecting rim ; both 

 pieces presenting a subtrigonal general outline, though really 

 hexagonal, if we count the slightly salient angles between the 

 shallow sinuosities in the upper margins; columnar facet small, 

 round, or a little oval. Radial pieces large, longer than wide, 

 presenting an oblong outline, slightly wider above than at the 

 base; all more or less convex on the inferior margin, which in 

 the anterior ray is provided with an obtuse mesial angle ; sinus 

 in the upper edge of each, for the reception of the succeeding 

 range of plates, near one-third as wide as the superior margin, 

 and excavated down about one-fifth the length of the plate, its 

 lower edge projecting rather distinctly outwards. First anal 

 plate as large as the first radials, and having much the same 

 form, excepting that it is provided with a distinct mesial angle 

 above, as well as below. 



Each first radial, as well as the first anal plate, has an ob- 

 scure, rounded prominence, extending down the middle to its 

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