26 CATALOGUE OF THE BLASTOLDEA. 



Stephanocrinus, however, and especially in S. angulatus, the elongated limbs of each 

 radial diverge rather widely so as to form a capacious radial sinus (PL XIX. figs. 8-11). 

 But this is not occupied by an ambulacrum descending from a peristome on a level 

 with or above the ventral ends of the radials as in the Pentremitidse ; for the 

 course of the ambulacra is almost horizontal, the peristome from which they start 

 being nearly on the same level as the more or less distinct lip which marks the point 

 of separation of the two limbs and the termination of the ridges which extend 

 upwards from the dorsal surface of the calyx. The ambulacra thus lie at the bottom 

 of a sort of funnel with deep notches cut in its rim, every two notches being sepa- 

 rated by a prominent interradial process, of which the outer part is formed by the 

 adjacent limbs of two contiguous radials and the inner part by a deltoid piece 

 (PI. XIX. figs. 8-12). The lower part of one of these prominent interradial processes 

 is shown in fig. 11, but they are very rarely found preserved entire. 



In all the Blastoids, except the Astrocrinidse, the five radials are all equal and 

 similar, as the basals would be were there sutures in the two large ones beneath the 

 antero-lateral rays. But in the two remarkable genera which constitute this family 

 the paired basals are altogether different from the azygos one, and the single radial 

 which they jointly support is quite unlike its fellows (PI. XIX. fig. 5 ; PI. XX. 

 fig. 1 5). These again are of two kinds, those right and left of the azygos radial 

 being slightly different from the two which are opposed to it. Each of the four in 

 Eleutherocrinus has a deeply notched sinus and nearly vertical ambulacra (PL XIX. 

 figs. 4, 6). The azygos radial, however, is more like the radials of Codaster trilo- 

 batus (PL XIII. fig. 3), or of Cryptoschisma Schulzi (PL V. figs. 25, 26), and has no 

 notch for the short ambulacrum, which simply terminates against its ventral edge 

 without extending over this edge and down on to the side of the calyx (PL XIX. 

 figs. 5, 6). 



The same is the case in the flattened and more or less cruciform Astrocrinus. The 

 azygos radial is somewhat rhomboidal, and notched for the tip of its ambulacrum 

 (PL XX. figs. 15, 19, 20) ; while the four others group themselves into two pairs, in 

 both of which the two limbs of eacli radial are somewhat unequal (PL XX. figs. 1-4, 

 11-14, 17, 20). This is only natural in the two rays C and E, which are next to the 

 azygos one. But the adjacent limbs of radials A and B are often rather longer than 

 their fellows, and form an interradial process which lies between the anterior ambu- 

 lacra, and is more prominent than the two right and left of it. 



The fork-pieces of Pentremites were spoken of by Say as the " scapulas," the term 

 employed by Miller for the first radials of Platycrinus, this being the type to which 

 Say considered Pentremites to be most closely allied. Roemer 1 in like manner 

 pointed out the resemblance of these plates to the radials of the Crinoid, and they 



1 Aichiv 1' Xuturgesch. 1851, Jahrg. xvii. 1M. i. p. 344. 



