16 PROCEEDINGS OF THE AMERICAN ACADExMY 



The Corresponding Secretary presented, 'from the authors, 

 the following- paper : — 



Description of tivo neiv Genera and eight neio Species oj 

 Fossil Crinoidea, from the Mocks of Indiana and Ken- 

 tucky. By S. A. Casseday and S. S. Lyon. 



DICHOCRINUS, Munster. 



In a resume of this genus by MM. De Koninck and Le Hon, they 

 state that, up to the appearance of their work,* only three species of 

 this genus had been described ; they add six, which, together with 

 eleven described by American geologists, make in all twenty spe- 

 cies. This comprises all the species of which we have any personal 

 knowledge. 



Heretofore much uncertainty has existed as regards the number 

 and disposition of the radials and the arms. De Koninck and Le Hon 

 give the following formula : — 



Basal pieces ... 2 

 Radial pieces . . . .4x5 

 Inter-radials . . . Unknown. 



Anal piece .... 1 Known. 



Arms . . . . .10 



Dr. B. F. Shumard, in some remarks about this genus, states as 

 follows: — "The anatomical structure of a very perfect specimen of 

 this genus corresponds only in part with the above formula. In our 

 fossil we find a base of two pieces, supporting a circle of five large 

 radials and one large anal piece, as in aU known species of this genus. 

 The radials however, are not repeated, but each one immediately gives 

 rise to two brachial pieces, which are pentagonal, and in turn support, 

 each, two simple arms ; so that the number of the latter amounts to 

 twenty." t 



The Messrs. Austin, who up to this time have figured the most 

 perfect examples of the genus, represent the number of radial pieces 

 to be twenty, i. e. " five repeated four times." 



" In D. ovatiis there appear to be but ten, i. e. five repeated twice ; 



* Recherches sur le» Crinoides. 



t Trans Acad. St. Louis, Vol. I. No. 1, p. 71. 



