170 Dr. G. J. Hinde on a 



developed (PL VI. figs. 13, 14). The distance between the 

 whorls varies from 5 to 14 raillim., but with only the short 

 detached fragments which I possess it is not easy to deter- 

 mine satisfactorily if there were regular intervals between the 

 whorls. The whorls are unequal in size ; and whilst in some 

 the cirri, or their bases, are large and apparently full-grown, in 

 others the cirrus-bases are very small and apparently imperfect. 

 In several instances there is a distance of about 14 millim. be- 

 tween the whorls or nodes of perfectly developed cirri, and 

 between each of these, though not centrally, there is a node 

 of imperfectly developed cirri (PI. VI. fig. 13). It would thus 

 appear that in this genus whorls of cirri are developed 

 on some of the intercalated joints between the larger nodes, 

 which indicates a different mode of growth from that which 

 prevails in the recent. Pentacrinidae. According to Dr. P. 

 Herbert Carpenter* the youngest nodes are always at the 

 top of the stem in this family, and all the joints subsequently 

 intercalated between them are internodal. 



As a rule there are five cirri in each whorl, but in some cases 

 only four are developed ; the space, however, in which the 

 fifth should appear is vacant and marked by a slight cicatrix. 

 Though normally the cirri of the same whorl are at the 

 same horizontal level, yet instances occur in which one or 

 more of the cirri are situated on joints higher or lower on the 

 stem than those bearing the others. Similar abnormalities 

 have been shown by Dr. P. H. Carpenter to be present in 

 the recent Pentacrinidae. Thus in Pentacrinus decorus, Wyv. 

 Thomp.f, and in Metacrinus cingulatus, H. Carp. J, the ab- 

 sence of a single cirrus is not at all unfrequent ; and further, 

 in Pentacrinus alternicirrus , H. Carp.§, the cirri of a whorl 

 are distributed on two nodal joints, and in a much more 

 regular manner than appears to be the case in Hystricrinus. 



The whorls in this genus are not, as is usually the case 

 in the Pentacrinidae, developed nearly entirely on the lateral 

 surface of a single, in some respects specially modified, stem- 

 joint; but the individual cirrus appears to commence its 

 growth on one of the smaller joints or rings (which must 

 have been penetrated by the cirrus-canal), and then extends 

 above and below it, so as to cover over the space between 

 two or three of the larger rings and the intervening smaller 

 ones. In the whorls of the larger cirri the stem-joints are 

 nearly entirely concealed by the cirrus-sockets, but they 



* Report on the Criiioidea. Voyage of H.M.S. 'Challenger,' p. 16. 



t See Report on the Crinoidea, p. 12, pi. xxxvi. fig. 1. 



% Id. p. 349. § Id. p. 12, pi. xxv. 



