REPORT ON THE CRINOIDEA. 283 
prominent and triangular or pentagonal in shape (Pl. XXV.). The same difference 
appears in Pentacrinus miilleri. The specimens in the Copenhagen Museum, one of 
which is figured by Liitken,’ have a closed ring of pentagonal basals. Some of those 
dredged by the “ Blake” are in the same condition; but this is far from being the case 
in the three individuals figured in Pl. XIV. and in Pl. XV. figs. 1, 2. Sir Rawson 
Rawson’s specimen (Pl. XV. fig. 1) has the smallest basals that I have yet seen in this 
species ; while I have met with all intermediate stages between this condition and that 
of Oersted’s types at Copenhagen. 
There is also a certain amount of variation in Pentacrinus blake, though | have not 
seen a sufficient number of specimens to be able to say much about it. In Pentacrinus 
naresianus, again, some individuals have pentagonal basals forming a closed ring ; while 
in others the basals are triangular and barely meet their fellows. But as a rule their 
outer ends are comparatively small and separated by the radials, which are sometimes 
prolonged slightly downwards over the upper stem-joints (Pl. XXVIII. fig. 1; Pl. XXX. 
fig. 1). A few specimens exhibit both conditions, some of the basals meeting their 
fellows, while the rest are separated by the downward projecting radials. 
But the most remarkable variations in the development of the pieces of the basal 
ring occur in Pentacrinus decorus. They are sometimes smaller than those of Penta- 
crinus asterius, and scarcely more conspicuous than the interradial ridges on the stem 
beneath them (Pl. XXXIV. figs. 1, 8; Pl. XXXV.; Pl. XXXVI. fig. 3); or they may be 
larger rhomboidal knobs standing out prominently from the general plane of the calyx, 
and meeting one another by their extended lower angles (Pl. XXXVI. fig. 1; 
Pl. XXXVII. figs. 1, 2); or they may present any intermediate condition between these 
two. To some extent these differences are perhaps due to age, both the individuals 
figured on Pl. XXXYV. being very young. But those represented in Pl. XXXVI. are 
apparently of about the same age, so far as can be judged from the characters of the 
stem, while their basals are at the two extreme stages of development; and the original 
of Pl. XXXIV. fig. 1 is very far from being a young individual! In the young 
Pentacrinus wyville-thomsoni, again, the basals are of about the same relative size as they 
are in the adult (Pl. XVIII. figs. 1-3). I do not, therefore, see any reason for regarding 
the variations in the development of the basals as of any more importance than the 
differences in the number of arm-divisions. In Actinometra parvicirra the number of 
arms may vary from thirteen to thirty-nine, and much the same is the case in some 
species of Pentacrinus and Metacrinus. But these differences are rarely of specific, and 
much less of generic value; and in the same way I find it impossible to consider the 
presence of a closed basal ring as a valid generic character separating Cacnocrinus from 
Pentacrinus. There is no recent Pentacrinus in which the basals do not appear upon 
the exterior of the calyx, so as to separate the radials either wholly or partially from the 
1 Om Vestindiens Pentacriner, loc. cit., Tab. iv., v., figs. 1, 2. 
