50 CALAMOCRINUS DIOMED/E. 



crinus), as well as Calauiocrinus and Bathycrinus, must have lived upon 

 rocky bottom, upon which their solid expanding conical base became firmly 

 attached. In the case of the Pentacrinidaj which I dredged in the West 

 Indies, they were most abundant at St. Vincent and Barbados, on I'ocky 

 ledges where nothing but the " swabs " of the bar and tangle were of 

 much use in bringing up specimens. 



Stems of some Fossil Crinoids. 



Thus far little attention has been paid to the mode of origin of new 

 stem joints. According to Thomson, new stem joints are added immediately 

 below the centrodorsal plate in the Pentacrinoid of Comatula3. Carpenter 

 has figured the mode of development of the young joints in Pentacrinus 

 Wyville-Thomsoni (Chall. Kep., Plate XXII.) both as young joints appearing 

 on the top of the upper stem joint for the time being, and as intercalated 

 joints either of nodals or internodals. Quenstedt has done the same for 

 E.xtracrinus (Plate 101, Fig. 24"). I .shall pass rapidly in review the 

 figures which have been published of the j^i'incipal tj'pes of stems among 

 the fossil Crinoids, to facilitate hereafter the comparison of the mode of 

 growth of the stem of palaeozoic with that of the recent Crinoid.s. 



The origin of new stem joints apparently varies greatly in the different 

 groups, and modifies to a considerable extent the appearance of the upper 

 part of the stem. 



Every wi'iter on the Ichthyocrinidne has noticed the difference in the 

 aspect of the upper part of the stem, which tapers considerably downwards, 

 an'd is composed of .short and even joints, which are followed abruptly by 

 alternate high and short pieces, new joints being apparently formed some- 

 what below the twelfth plate. 



The stem of Millericrinus Pratti varies very considerably, as has been 

 shown by Carpenter,* who has described a series of stems varying from 

 the pedunculate to the free mode of existence (Plate I. Figs. 5-8, 10, 

 12, 14), the majority of the stems tapering rapidly from above downwards, 

 the last joints seeming to have fused. The mode of intercalation of what 

 he considers as new joints in proce.ss of formation (Plate I. Figs. 1, 7, 10) 

 is diffei-ent from tlie process by which new joints force tlieir way to the 

 surface between the older joints in Calamocrinus. 



* P. H. Carpenter. On some new or little known Jura-ssic Crinoids, Q. Jouru. Geol. See, 1882, Vol. 

 X\X\III. p 3l'. 



