Summit Structure of Peniremites. 501 



portance, as many of them appear to be, the specific dis- 

 tinctions will be principally confined to the variations in 

 the general shape, the mode of bifurcation of the arms, 

 and the form and arrangement of their joints, and the 

 form, arrangement, and ornamentation of the plates of 

 the body and the ventral sack. 



The three species of this genus at present recognized 

 are the Poteriocrinus di/atatus, and P. ventricosus, of Hall, 

 and CcBliocrinus subspinosus herein described, all from the 

 Burlington limestone. 



Caeliocrinus subspinosus (n. s.) Body small, broadly ex- 

 panding ; basal plates small, showing minute pentagonal, 

 or subtriangular faces beyond the margin of the column; 

 subradials of moderate size, about as wide as high, three 

 hexagonal, and two heptagonal ; first radials a little larger, 

 and more massive than the subradials; they are rather 

 prominent above, where they are separated from each 

 other by moderately deep sutures ; second radials larger 

 than the first, the anterior and posterior ones larger than 

 the other two. The arms bifurcate but once or twice, the 

 second bifurcation being so near the ends of the arms as to 

 be liable to be broken off. The first four anterior arms bi- 

 furcate on the tenth, and the other six on the eighth joint 

 from the second radial. Surface of the body and arms 

 without ornamentation, the latter rounded, or subcylindri- 

 cal. The column moderately strong, round, and composed 

 of thin plates of nearly equal size. The ventral sack, 

 which reaches nearly as high as the arms, is proportionally 

 smaller than in C. dilatatus, and C. ventricosus. The top, 

 which is the only part distinctly visible in our specimen, 

 is flattened, the plates composing it not very numerous, 

 tumid, and four or five of them at the margin are produced 

 into short, diverging spines. The arrangement of the anal 

 series is the same as mentioned in the generic descrip- 

 tion. 



