232 Mr. F. A. Bather on British Fossil Cnnoids : 



Messrs. Waclismuth and Springer have appai-ently found out 

 for themselves * by this time that Angelin's description of 

 Sagenocrinus was, so far as the number and position of the 

 plates were concerned, perfectly correct : this is not the place 

 to discuss the matter, but the sixth plate in the basal circlet 

 does alter all appear to be an " anal." 



That the structure of Carahocrinus was in all essentials 

 correctly described by Billings, Messrs. Wachsmuth and 

 Springer subsequently admitted f ; but with their pronounced 

 views as to the extreme improbabdity of an anal or a radial 

 descending into the basal circlet, they naturally slurred over 

 the importance of that structure. This was their explana- 

 tion : — ^' The small plate within the basal ring, which is only 

 known in this genus, is, we think, a supplementary azygous 

 plate of no fundamental importance, a plate bearing to the 

 regular azygous plate similar relations as the small accessory 

 interradials in some specimens of Archieocrinus sculptus to the 

 regular interradials/' Now, however, Thenarocrinas enables 

 us to look at Carahocrinus from a different standpoint ; the 

 supplementary plate may very naturally be regarded as a 

 portion of the radianal, just as the radianal itself is a portion 

 of the right posterior radial ; so that, were this supplementary 

 plate again united to the radianal, we should have a dispo- 

 sition of anal plates very similar to that which obtains in 

 Thenarocriiuis. 



It was this similarity in a structure so dissimilar to that of 

 all other Fistulata that led me, w^hen discussing the classifi- 

 cation of the group, to place Thenarocrinus alongside of Gara- 

 hocrintts. It is no doubt conceivable that this structure, 

 peculiar though it is, may have been arrived at along two dif- 

 ferent lines of descent. There are, however, yet other points of 

 resemblance, in the diehotomous branching of the arms, the 

 number of the costals, and the structure of the column. The 

 only important difference between the two genera lies in the 

 greater breadtli and length of the arms in Thenarocrinus ; but 

 this is no great difference for two forms so widely separated 

 in time and space. The more globular shape and generally 

 radiate ornamentation of the dorsal cup, exhibited by the 

 described species of Carahocrinus, go for nothing, for they do 

 not obtain in two specimens of that genus kindly lent me for 

 examination by Dr. G. J. Hinde. 



Whether these considerations warrant the establishment of 



* W. & S., " Discovery of the Ventral Structure of Tuxocrinus Sec, " 

 Proc. Acad. Nat. Sci. Philadelphia, 1888, p. 357. 

 t Rev. III. (217), Proc. 1886, p. 141. 



