194 PROCEEDINGS OP THE ACADEMY OP [1886. 



upper margins constitute fully three-fourths of the periphery at 

 the top of the radials, occupy together less than one-half of the 

 circumference of the basal cup. This disproportion is caused b}'- 

 the peculiar form of the other radials, which, notwithstanding the 

 great spreading of the calyx, diminish in width upwards. The 

 anterior radial is much smaller, heart-shaped, with strongl}- con- 

 vex lateral edges, which converge almost to a point at the top of 

 the cal^'x. The basi-radial suture is somewhat concave, and fully 

 as wide as that of the larger plates. The two postero-lateral 

 radials together are very little larger than the anterior one ; that 

 toward the right is smaller, very narrow, wider at the bottom 

 than at the top, and triangular when the sides are straight ; but 

 when these are curved, which is moi^e frequently the case, it is 

 somewhat lunate. The other radial is quadrangular, fully twice 

 as high as wide, and of equal width throughout. 



The articular surface of the radials is provided with conspic- 

 uous grooves and intervening ridges, the former with a depres- 

 sion near the outer margin of the plate. The grooves along the 

 surface take a tortuous or undulating course, and near their inner 

 end turn rather abruptly toward the anterior radial. The latter 

 plate has generally but one groove, which is deeper than any of 

 the others and perfectly straight, but when it has two grooves, as 

 is exceptionally the case in Catillocrinus Tennessese^ these unite 

 before entering the inner cavity. The two larger radials contain 

 numerous grooves the number varying with the species that 

 toward the right, as a rule, has more than the one on the left. The 

 former radial has been observed to have in G. Tennesseae 27 to 31 

 grooves, in C Wachsmuthi 16 to 20; the plate toward the right 

 in the former species has from 21 to 23, the opposite one 15 

 grooves. The two small irregular radials have, so far as observed, 

 only one groove each. 



In perfect specimens, the grooves are lined by two rows of 

 short, transverse pieces, which partly cover the groove, but leave 

 underneath a good-sized passage. The plates rest upon the ridges, 

 whei'e they abut against their fellows from adjoining grooves. 

 With the exception of the ridges and grooves, the truncated 

 upper side of the radials forms a uniform plane, interrupted only 

 by a small elevation along the left side of the quadrangular radial. 

 This elevation is occupied by a small, elongate anal plate, which 

 abuts against the two proximal joints of adjoining arms. The 



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