174 



THE CRINOIDEA 



details), Silurian to Carboniferous, world-wide. This, being the best 

 known genus of the sub-order, demands closer description. The dorsal 

 cup (analysed in Fig. LXXXIX. 5) consists of: 5 equal IBB ; 5 large 

 BB, all hexagonal except post B, which is truncate above ; 5 shield- 

 shaped RE, each with a facet usually \ width of plate, the articular 

 surface being either smooth and imperforate, or having a slight transverse 

 ridge pierced by the axial canal (Fig. LXXXIX. 2); a square anal x, in 

 line with RR and resting on truncate post. B. Tegmen consists of 5 O 

 resting on the incurved shoulders of RR, and surrounding a pentagonal 



O O 



Fi<:. LXXXIX. 



Cyathocrinw. I, C. muUibnuhiatvt, seen from posterior. (Brit. HIM. E5402.) 2, radial 

 of C. visbycensit, showing articular facet, x 2. 3, joint-surface of columnal of C. acinotubut, 

 x 2. 4, joint-stirface of a brachial of same, with covering-plates in position, x 9. 5, analysis 

 of the cap. a.c, axial canal ; /, fulcral ridge ; t, intercalated plate ; j, joint-surface ; t.c* and 

 I c* the twp halves of a covering-plate of the left side ; nn, nodals ; r.c 1 , proximal half of a 

 covering-plate of the right side ; t, anal tube ; v. g, ventral groove. (2-5 after Bather.) 



peristome (Fig. XXXIX. 1); post. O being large, conspicuous, and pierced 

 by numerous water -pores, the other being smaller and often almost 

 entirely hidden, partly by ambulacrals resting on the apposed edge of all 

 O, partly by small interambulacrals (Fig. XXXIX. 2). The proximal Amb 

 meet over the peristome and often grow to a large size, sometimes fusing 

 and simulating orals (for which elements they are taken by W. & Sp., 

 see Fig. XLIII.). The anal tube consists of more or less hexagonal plates, 

 arranged in fairly regular longitudinal rows ; it varies greatly in width, 

 length, and width of lumen ; the anus is at its distal end ; the plates may 

 be slightly folded, but are not transversely elongate, nor are there pores, 



