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REPORT ON THE CRINOIDEA. 311 
seems scarcely possible, though the development of a new visceral mass inside the calyx 
iS not uncommon. 
As in Pentacrinus asterius, there is a considerable variation in the development of the 
basals. In the Copenhagen specimens described by Liitken, 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 
rhomboidal or triangular in shape, but only just meeting one another in the re-entering 
angles of the calyx (Pl. XIV.; Pl. XV. fig. 2); while in Sir Rawson Rawson’s specimen 
they are small and inconspicuous (Pl. XV. fig. 1), 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; but 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 axillaries, there is comparatively little room 
for the arms, the bases 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 which indicates a 
tendency to variation in the direction of Metacrinus with its five or eight primitive radials 
(Pl XXXIX. fig. 1; Pl. XLVI). 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. XLII. fig. 4). 
The plating of the disk of Pentacrinus miillert (Pl. XVII. fig. 10), like that of 
