24 CATALOGUE OF THE BLASTOIDEA. 



its outer surface may be regarded as composed of two parts, namely — the body, which 

 extends from the basiradial suture up to the radial lip, in which the ambulacra 

 terminate ; and the limbs, which reach upwards at the sides of the ambulacra until 

 they meet the outer ends of the oral crests. The adjacent limbs of contiguous radials 

 are thus produced upwards between the ambulacra, and the general aspect of the 

 calyx depends upon their relative length and upon the convexity of their surface 

 more than upon any other point in the character of the radials. 



In Codastcr pyramidatus and in C. Hindei the radial limbs are quite short, so that the 

 sinus is wide and shallow ; and the intervening oral crests slope downwards from 

 the mouth, which is at a higher level than the interradial angles of the calyx (PI. XII. 

 figs. 2, 5). The spade-like radials of Codaster trilobatus cannot be said to have any 

 limbs at all, and the term fork-pieces is hardly applicable to them (PL XIII. figs. 

 3, 9-12), while the mouth and oral crests are at much the same level. But in C. alter- 

 natus, var. elongatus, the radial limbs are longer, the sinuses deeper and more steep- 

 sided, and the oral crests actually slope downwards towards the mouth (PI. X. fig. 20). 

 The same is the case in Phcenoschisma Vemeuili and P. Archiaci (PI. XI. figs. 5, 6 ; 

 PL XII. fig. 10; PL XIV. fig. 8); while in P. nobile, P. caryophyllatum, and 

 P. acutum the mouth and oral crests are in nearly the same plane (PL XI. fig. 2 ; 

 PL XIV. figs. 1, 10). The radials of these species and especially of P. caryophyl- 

 latum are very much incised ; but the sinuses, though deep, are relatively wide and 

 not completely filled by the ambulacra, so that parts of the hydrospire-clefts are still 

 visible on their walls. 



A parallel series of variations in the shape of the radials is presented by the 

 genera Cryptoschisma and Pentremitidea, in which, as in Phcenoschisma and Codaster, 

 the deltoids are confined to the summit, not appearing at all on the exterior of the 

 calyx. The radials of Cryptoschisma Schulzi are almost as spade-like as those of 

 Codaster trilobatus (PL V. figs. 25, 2G). But their ventral surface, on which the 

 hydrospire-slits are situated, is concealed by the broad ambulacra (PL V. figs. 23, 

 24 ; PL XIII. fig. 20). Between these are the oral crests formed by the deltoid 

 pieces very much as in Phcenoschisma acutum (PL XIV. fig. 11). In Pentremitidea 

 PaiUettei(Y\. IV. fig. 9 ; PL XIV. fig. 13) and P. Lusitanica (PL IV. fig. 11 ; PL V. 

 fig. 20) the radials are more distinctly convex and spread outwards above the basal 

 cup, so that although there is a moderately long sinus it does not extend very far 

 down towards the basiradial suture. On the other hand, in Pentremitidea angulata 

 (PL IV. fig. 18), P. Wachsmuthi (PL V. fig. G), P. Gilbertsoni (PL V. fig. 9), and 

 P. lcda\ (PL V. fig. 12) the radials are deeply notched, very much as they are in 

 Phcenoschisma caryophyllatum (PI. XIV. figs. 1, 4). 



In Pentremitidea and Phcenoschisma (PL IV. figs. 9, 11, 13, 18), as in Codaster 

 (PL XII. figs. 2, 5) and Cryptoschisma (PL V. figs. 23-26), the radials form the 

 whole external surface of the calyx in its interradial regions ; for the deltoids are 



