PART 5 A MONOGRAPH OF THE EXISTING CRINOIDS 821 



The cirri are unknown. 



The narrowly visible basals are nearly uniform in height throughout their whole 

 width, but are slightly arched in form. The apex of each arch is internulial, and the 

 very small interval between it and the notched edge of the centrodorsal below is occu- 

 pied only by perisome. Hence, the basal ring is really only in contact with the centro- 

 dorsal at its 5 lowest points, that is, at the interbasal sutures, immediately beneath 

 the middle of the radials. 



The radials are barely half as long as the IBr, though twice as long as the basals; 

 they have exceedingly high muscle plates projecting inward. 



The IBr, are about as long as broad, with the distal border incised to receive the 

 backward projection from the IBr 2 (axillaries). The sides of the IBr, are slightly 

 flanged and the adjacent ones are nearly in apposition; except at the distal end where 

 they converge abruptly, the sides are parallel. The proximal half of the axillary is 

 narrower than the main part of the IBr, but widens abruptly in the middle of its length 

 to define a distinct pore between adjacent division series. A similar but smaller pore 

 is formed between the first two pairs of brachials. 



There are 10 smooth, cylindrical arms, all broken at or before the third syzygy 

 (9 + 10). 



The first brachials are well separated laterally, and have their inner sides much 

 shorter than the outer; the distal border is incised to receive the strong backward 

 projection from the quadrate second brachials. The following brachials have markedly 

 unequal sides. 



Syzygies usually occur between brachials 3+4, 6 + 7, and probably 9+10 but 

 are often irregular in position. The length from the proximal edge of the IBr, to the 

 second syzygy at brachials 6 + 7 is 8 to 8.5 mm. The width at brachials 3+4 is 1 .7 mm. 



No pinnule-bearing brachials remain. 



The disk is almost naked, 4 mm. in diameter. The mouth is somewhat excentric 

 and is surrounded by a large peristome, immediately behind which is the anal tube. 

 The brachial ambulacra lie close down upon and between the muscle bundles. 



FIGURE 52. Aldicrinus ayvilli P. H. Carpenter, holotype. 



4 mm 



