REPORT ON THE CEINOIDEA. 311 



seems scarcely possible, though the development of a new visceral mass inside the calyx 

 is not uncommon. 



As in Fentacnnus asterius, there is a considerable variation in the development of the 

 basals. In the Copenhagen specimens described by Lutken, and in some of those which 

 I have examined, they are pentagonal in outline and form a closed ring separating the 

 radials from the top stem -joint. In other forms they are more prominent and 

 rliomboidal or triangular in shape, but only just meeting one another in the re-entering 

 angles of the calyx (PL XIV.; PI. XV. fig. 2) ; while in Sir Rawson Rawson's specimen 

 they are small and inconspicuous (PL XV. fig. l), as in some varieties of Pentacrinus 

 decorus (PL XXXVI.). 



The number of arms may vary from thirty-five to forty-five, some individuals occa- 

 sionally having ten arms to the ray. Generally, though not invariably, the axillaries are 

 limited to the outer arm of each pair in the manner already described ; Ijut I have not 

 seen any individual in which the six- or eight-armed arrangement is constant on every ray. 



As there are very few joints separating the axUlaries, there is comparatively little room 

 for the arms, the liases of which are therefore more or less flattened laterally, both 

 in the outer and in the inner parts of the rays. In fact, wherever an axillary occurs the 

 two arms which it bears have their inner faces flattened, while the outer sides of the rays 

 are flattened continuously from the second radials to as far as some six or eight joints 

 beyond the fifth axillary. 



This feature is especially marked in two fine specimens from the " Blake" collection, 

 which are also distinguished by the shape of their lower pinnule-joints. One is from 

 Martinique and the other from Barbados. The calyx and arm of the former are repre- 

 sented on PL XV. figs. 2, 3. The outer edges of the joints from the second radial 

 onward are produced somewhat sharply upwards, and fit closely against those of adjacent 

 joints. This is less prominent in the Barbados specimen, which shows an occasional 

 tendency towards carination of the arm-bases. The other form is remarkable for the 

 abnormal condition of one of its rays, as shown in PL XV. fig. 2. The third radial is 

 articulated to the second instead of being united to it by syzygy. But it is itself a 

 syzygial joint; so that there are primitively four radials, a character wliieli indicates a 

 tendency to variation in the direction of Metacrinus with its five or eight primitive radials 

 (PL XXXIX. fig. 1 ; PL XL VI.). The pinnules of these two individuals are also different 

 from those of other examples of the type. They are generally composed of moderately 

 broad, flattened joints, the lowest of which are somewhat stouter than their successors. 

 But in the two " Blake " specimens the pinnules are less flattened than usual, and the 

 lower joints markedly trihedral in form, recalling, though in a less degree, the prismatic 

 shape of the pinnules, which is characteristic of Metacrinus (PL XXXIX. fig. 1 ; 

 PL XLIII. fig. 4). 



The plating of the disk of Pentacrinm mulleri (PL XVII. fig. 10), like that of 



