THE STEM Wl> CAL1 \. ] 1 



summit so as almost or quite to reach the broad flattened base (PL II. figs. I-."., 1 I 

 17, 32-35 ; PL III. fig. 4 ; PL VIII. figs. 1, 14, 16, 10 ; l'l. IX. tigs. 1, 2). h. 

 other species again die I'onn is more or less globular (1M. I X. figs. 6, 11, L2) ; ovoidal, 

 as in Eeteroblastus (PL VI. fig. 1), Elceacrinus (PL II. figs. 43, 46; PL XVIII. fig. 

 19), and Eleutherocrinus (PL XIX. figs. 4, 5), or even much elongated. But in all 

 cases alike the ambulacra extend from one end of the calyx to the other, their proximal 

 ends lying along the sutures of two deltoid plates, while their distal ends are received 

 into the more or less deeply incised radials which surround the circle of small and 

 somewhat flattened basals ( PL VIII. figs. 3, 8, 13, IS ; PL IX. figs. 3, 4, 9, 13). But 

 in a large number of Pentremites, of which J', pyriformis is a good type (PL II. figs. 

 24-30), the basals are prolonged into a conical cup, and the radials are much less 

 deeply incised to receive the ambulacra, so that the latter do not nearly extend along 

 the whole length of the calyx. This is the casein the genera Codaster, Orophocrinus, 

 Phcenoschisma, Oryptoschisma, Pcntremitidea, Troostocrinus, and others (PL IV. figs. 9, 

 11, IS ; PL V. figs. 1, 3, G, 9, 17, 20, 21, 25, 26 ; PL XII. figs. 2, 3, 5, 6, 10, 11 ; 

 PL XIV. figs. 1, 4, S, 10, 13, 14, 17 ; PL XV. figs. 1, 3, 6, 9 ; PL XIX. fig. 13). In 

 types such as these the basals and the bodies of the radials form a cup which expands 

 gradually from below upwards till it reaches its greatest diameter between the lips of 

 the radials, in which the ambulacra terminate; while their limbs and the deltoid 

 pieces together make up a more or less flattened dome, in the centre of which the 

 mouth is placed. In some species of Orophocrinus and Pcntremitidea this dome is 

 almost hemispherical in outline (PL IV. figs. 13, 18 ; PL XV. figs. 1, 3, 6) ; while in 

 other types it has the form of a truncated cone (PL V. figs. 3, 17, 21 ; PL XII. fig. 11 ; 

 PL XIX. fig. 13). In Crypfoschisma Schulzi and in Cadaster trilobatus this disappears 

 altogether, and the ventral surface is nearly flat (PL V. fig. 20 ; PL XIII. figs. 3, 

 10, 12, 15) ; while in Stcplianocrinus, although the ambulacra occupy a nearly hori- 

 zontal position, the interradial areas of the summit are produced into five prominent 

 angular processes (PL XIX. figs. 11, 12). 



Except in the Astrocrinidre (PL XX.) the general outline of the calyx, as seen from 

 above, is usually circular or pentagonal (PL IV. figs. 1, 14; PL V. figs. 7, 10, 13 ; 

 PL VI. figs. 2, 8, 16 ; PL VIII. figs. 4, 9, 12 ; PL IX. fig. 8 ; PL XII. figs. 1, 4). In 

 some species of Pentremitidea, however, there are more or less distinct reentering 

 angles between the ambulacra (PL IV. figs. 8, 10, 12 ; PL V. figs. 2, 4, 16, 23), a 

 character which culminates in Orophocrinus stelliformis (l'l. XV. fig. 11). Eleu- 

 therocrinus, although exhibiting a striking asymmetry in the character of its ambu- 

 lacra, has a tolerably regular ovoidal outline in horizontal section (PL XIX. fig. 6) ; 

 but in the allied genus Astrocrmus the want of symmetry extends into the rays, and 

 the outline is that of a more or less regularly four-pointed star, one ray of which is 

 often longer than the rest (PL XX. figs. 1, 7-14). 



The composition of the calyx varies very considerably among the different genera 



