PAL.B0NT0LOGICAL REPORT OF GEOLOGICAL SURVEY. 469 



riformis, and others, have severally three small plates or pieces, dis- 

 tinctly separated from the pieces heretofore designated as the "Basal 

 pieces;'''' these three pieces form the base of the cup, and as they lie be- 

 low the pieces heretofore recognized as basal, are true basal pieces, and 

 the others necessarily become first radials. It is therefore proposed to 

 amend the generic description, and the following formula is offered : 

 GENUS PENTREMITES. Say. 

 Generic Formula: 

 Basal pieces, lX-3? short, broad, and nearly of equal size. 



First radial pieces, lX^? two hexagonal, perfect; one pentagonal, 



and imperfect. 

 Second radial pecies, 1x5, nearly of equal size, long, forked. 

 Interradial pieces, 1X5? small, lanceolate, nearly equal in size. 

 Pseudambulacrse, 1X&? l° n g? filling the forked pieces, and ter- 



minating around the mouth. 

 Mouth, 1, central. 



Ovarial openings, 2x5, situated around the mouth. 



Column, cylindrical, perforated, segments luaeq size and thickness. 



PENTREMITES OBESUS. Lyon. 

 (Plato II. fig. I, la, lb, Ic, 1 d.) 



Body, elliptical half its heighth, rounded at the summit; the lower 

 part has the form of a broad inverted cone; the diameter is to the 

 heighth as 4 is to 5, (nearly.) Basal pieces, of equal size, sub-quad- 

 rangular, of similar form, low, broad ; sides diverging upwards from 

 the columnar articulation; greatest heighth at the line of junction 

 with each other; irregularly concave, upper margin, into which the 

 first radials are fitted, regularly concave at their junction with the 

 column ; when joined, they form a low cup, concave at the base, the 

 upper margin forming an unequal sided triangle. 



First radials two, of equal size, hexagonal ; the third pentagonal, 

 and a little larger than half the size of the hexagonal pieces; this 

 unequal piece probably indicates the anal side of the pentremite ; 

 the three pieces, when joined, present a broad shallow cup, the superior 

 margin of which is marked by five broad angular points, between which 

 are three angular, and two irregular, concave depressions, the latter 

 being upon the summits of the hexagonal pieces. 



