REPOET ON THE CRINOIDEA. 283 



prominent and triangular or pentagonal in shape (PL XXY.). The same difference 

 appears in Pentacrinns iniilleri. The specimens in the Copenhagen Museum, one of 

 which is figured l)y 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 PI. XIV. and in PL XV. figs. 1, 2. Sir Rawson 

 Eawson's specimen (PL XV. fig. 1) has the smallest basals that I have j&t 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 hlahei, though I have not 

 seen a sufficient number of specimens to be able to say much about it. In Pentacnnus 

 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 XXVIIL 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 XXXV. 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 tvyviUe-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 Actinomctra 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 Metacriniis. 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 Cainocrinus 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. 



