III. Thenarocrinus calUpygus. 231 



of the ossicles along radial lines is often observable, as in 293 

 Holcroft and 138 Mason College (Diagram 7)._ 



The Dudley specimen shows slight longitudinal ridges on 

 its stem, especially at the proximal end; and these as they 

 cross the transverse ridges of the ossicles produce a slight 

 cancellated pattern (Plate X. fig. 7). For the present, at all 

 events, it is best to regard this as a mere individual variation. 



General Remarks. 



The most interesting feature of this genus is that in which 

 it differs from other Fistnlata, namely the low position of the 

 Radianal. Indeed this one point alone separates it from 

 nearly all other Crinoids, and appears of still further import- 

 ance in connexion with various utterances of Messrs. Wachs- 

 muth and Springer. Criticising the description of Garabo- 

 crinus by E. Billings, they wrote : '' The anal area, .... 

 according to Billings, is composed of three plates, the lower 

 one resting upon the underbasals, which is in itself an anomaly 

 such as is found in no other genus " *. For the same reason 

 they denied the correctness of Angelin's description of Sageno- 

 cri/ius, saying, " Angelin gives the number of basals (para- 

 basals) as six, which is evidently a mistake, nor do we believe 

 that the sixth plate represents an anal plate, as no plate of 

 that kind has ever been observed below the line of radials " !• 

 Again in 1885 they wrote with even more decision, " There 

 is not a single instance of Crinoids known to us where either 

 a radial or an anal plate entered the basal ring " J. There 

 does not, however, seem to be any morphological objection to 

 the sinking of an anal plate into the basal circlet, and in fact 

 Messrs. Wachsrauth and Springer have prudently refrained 

 from a jjri'ori argument. There can at any rate be no manner 

 of doubt that the thing has happened in Theiiarocrinus, and, 

 rare though it be, there is nothing anomalous about it ; on the 

 contrary, the sinking of the radianal, in common with the 

 brachianal and anal series, is in perfect harmony with the 

 views as to the origin of those plates put forward in Paper II. ; 

 while the consequent widening of the anal area, enhanced as 

 it is by the width of all the plates of the dorsal cup, is 

 obviously correlated wuth the large size of the ventral sac, just 

 as was explained on pp. 319 and 330 of the same paper. 



But if Thenarocrinus is not anomalous, neither is it unique. 



* Kev. I. (144), Proc. 1870, p. 367. 



t Rev. II. (202), Proc. 1881, p. 376, footnote. 



X Rev. III. (55), Proc. 1885, p. 277. 



17* 



