4S SIK C. WYVTLLE THOMSON" OK NEW LIVING 



sculpture of the plates and joints, that the first named of the 

 two species now to be noticed must be referred to the same genus. 

 There is, however, one marked diiFerence between the two : in 

 our specimen of B. gracilis, which looks as if it were full-grown, 

 the ten arms are perfectly simple, and there is no trace of pinnules, 

 while in B. aldrichianus the pinnules are well developed. 



Aslhave already said(Zoc. cit.), strong resemblances in the struc- 

 ture of the stem, in the structure of the base of the cup, and in the 

 form and arrangement of the ultimate parts of the arms associate 

 Bathycrinus with Mhizocrinus ; but the diiferences between the two 

 genera are very obvious. The radial axillary joints, which in Bhi- 

 zocrinus are contracted to support a single first brachial, are here 

 expanded and bear two articulating surfaces giving origin to two 

 arms ; so that, as in most Crinoids, the number of primary divi- 

 sions of the arms is ten. The structure of the cup and of the 

 upper part of the stem, while essentially the same in both, is dif- 

 ferent in detail : in Bhizocrinus the funnel-shaped piece formed by 

 the coalescence of the basals with the fused first radials above 

 and the dilated upper joint of the coalesced upper joints of the 

 stem beneath, makes up a large part of the cup ; while in Ba- 

 thycrinus the stem barely enlarges at its junction with the cup, 

 the ring formed by the basals is very small, and the first radials 

 are free from the basals, and often free from one another. The 

 oral plates, which are conspicuous in Bhizocrinus, are absent in 

 Bathycrinus. 



Syocrinus is a totally different thing ; but, as we shall see here- 

 after, it presents certain general resemblances and even certain 

 special correspondences in structure which seem to associate it 

 also with Bhizocrinus. 



There seems little doubt that Bhizocrinus finds its nearest known 

 ally in the chalk and tertiary Bou7^guettic7Hnus, and that it must 

 be referred to the neighbourhood of the Apiocrinidae. Were it 

 not that Bathycrinus and Hyocrinus are so evidently related to Bhi- 

 zocrinus, the characters of the Apiocrinidae are so obscure in the 

 two first-named genera that one would certainly have scarcely 

 been inclined to associate them with that group. 



They are both comparatively small forms ; and although they do 

 not show the peculiar tendency to irregularity in the number of 

 their principal parts which w^e find in Bhizocrinus, their calyces 

 are small in proportion to the size of the stem, so that there is still 

 a comparatively excessive development of the vegetative system. 



