REPORT ON THE CRINOIDEA. 



267 



Fig. 19. — The calyx and arm-bases of two specimens of 

 Rhizocrinus rawsoni from Panama ; x 4. In both cases 

 the cup is unusually wide in proportion to its height ; 

 and iu tlie riglit hand specimen (B) the grouping of 

 the lower brachials is very irregular. 



In a considerable number of individuals from different localities on both sides of the 



Atlantic, I have found the radials to be marked by a circular furrow of variable depth. 



It crosses the body of the radial at the level of 



the upper angles of the basals between which 



the radial rests, as is well shown in the young 



specimen represented on PI. LIII. fig. 8. 



In the more mature individual from the 



Caribbean Sea, shown in PI. IX. fig. 3, the 



furrow crosses the radials at about half their 



height ; while in one of the specimens from the 



neighbourhood of the Azores (Station 76) the 



basals are much less angular at the top, so that 



the radials are more nearly oblong and almost 



entirely above a rather strong constriction at 



the level of the basiradial suture (PI. X. fig. 3). 



Other individuals, however, are entirely desti- 

 tute of any indication of such a constriction. 



This is the case, for example, with those 



dredged by Captain Cole ofi" Panama, which 



are further remarkable, not only for the great 



relative width of the basal cup as shown in the woodcut (fig. 19), but also for the extreme 



variation in the position of the first pinnule. 



In one individual this is on the epizygal of the seventh brachial in two arms, on that 

 of the fifth in two others, and on that of the fourth in the remaining one. In four arms 

 of another specimen the epizygals bearing the first pinnule are respectively those of the 

 third, fourth, fourth, and fifth brachials ; while in a third individual three arms are normal, 

 with a pinnule on the third epizygal, the two others not bearing a pinnule till the next 

 (fourth) joint. Lastly, in a fourth individual every one of the arms is developed 

 abnormally. Three of them are shown in woodcut, fig. 19, B. I will not attempt to 

 ofi"er an opinion upon the grouj)ing of the syzygies and muscular articulations in this 

 specimen. But in one arm at least there appear to be two syzygies in succession ; so 

 that the composite brachial is in three parts instead of in two only. This is a variation 

 of some interest, as it is normal in the arms of Hyocrinus (PL VI. fig. 1). Both types 

 of brachial, that with one and that with two syzygies, occur in different species of the 

 Palaeozoic Heterocrinus, as pointed out already (ante, p. 53). 



Although the occurrence of Rhizocrinus rawsoni in the East Atlantic and its more 

 striking peculiarities, especially the length of the basals, were noticed in the first Eeport 

 upon the Caribbean Crinoids ^ which Prof. Perrier quotes, he was led to describe the 



' Bull. Mus. Comp. Zo'ol., vol. x., No. 4, p. 174. 



