28 PROCEEDINGS OF THE AMERICAN ACADEMY 



upon this are disposed the other pieces, one above the other, rapidly 

 diminishing to a point. 



Summit. The summit is divided into five fields ; the division line 

 appears to radiate from the centre of the summit to the centre of each 

 group of arms. Four of these fields are nearly alike ; the form and 

 the arrangement of the pieces in each are similar ; the fifth field, 

 which lies above the junction of the basal pieces, between the pairs 

 of circular depressions, supports a short rudimentary proboscis near its 

 centre, about .01 of an inch in diameter, and about .15 of an inch in 

 height, composed of a great number of small pieces (seventy to eighty). 

 The pieces covering the fields are of irregular size, the general form 

 inclining to triangular; some are quadrangular, one end of the piece 

 being much narrower than the other ; other pieces are elongated 

 octagons. 



Column. The column is round, delicate, composed of very thin 

 pieces, the alternate ones larger and smaller ; near the calyx the 

 column suddenly enlarges to its insertion into the. columnar pit. 



No surface markings are visible. 



Dimensions : — 



Height of basal pieces ..... .20 inch. 



" " first radial pieces 40 " 



" " second and third together ... .03 " 



Diameter of calyx ....... .45 " 



Length of arms ....... 1.00 " 



Diameter of column , . . . . . .02 " 



Geological position and locality. Rare, in the third limestone above 

 the base of the millstone-grit beds of Grayson Springs, Grayson County. 

 Its vertical range appears to be quite limited. 



Remarks. This elegant little crinoid is closely allied to Dichocrinus 

 and Pterotocrinus ; it differs from both genera in the number of 

 pieces forming the series resting on the basal pieces. The deepest 

 angular notch in the basis of both genera usually marks the anal side ; 

 in our genus the mouth is on the field, on the side directly opposite 

 the only angular notch in the basis. All the pieces rising from the 

 basals bear arms in our genus ; but this is also true of Dichocrinus 

 Ficus, which has six arm-bearing pieces, and no barren or non-arm- 

 bearing piece, termed anal piece in this genus. 



As genera and species are now defined, we are compelled to sepa- 



