410 Mr. F. A. Bather on British Fossil Crinoids : 



•with relics of tlieir ancestry still preserved by certain speci- 

 mens of B. decadactyhis in the branched first pinnule. We 

 have tiaced the gradual differentiation of these pinnules from 

 coarse to fine, from rounded to square-sided. We have seen 

 too the sutures between the arm-ossicles at first set at steep 

 angles alternately to one another, then with the angle lessen- 

 ing, and lastly quite parallel. Concomitantly with these 

 changes we have noticed how the plates of the cup, from 

 being smooth or simply rounded, have become more and more 

 folded along the axial lines, while the ventral sac has become 

 less ridged, and the stem more pentagonal. These species 

 afibrd us an excellent illustration of the gradual adoption by 

 the adult of the characters of old age. The cliaracters in 

 which the species differ from one another may be useless, but 

 they are not accidental ; they represent different stages of 

 growth. It is unfortunate that the horizon of B. jnnnulatus 

 is not quite certain ; if the specimen really comes from a bed 

 below that in \a hich the other British species have hitherto 

 been found, some doubt is cast on the truth of the above 

 views. But the agile evolutionist has leapt over worse 

 obstacles ere now, and it must be remembered that evidence 

 from only one specimen (as is also the case with B. ramosus) 

 is of sliglit value in such a question, while sou^ething may be 

 explained by the change from shale to limestone. (See Note, 

 p. 412.) 



lielatwn to other Genera. — Of the other genera placed by 

 me in the division Botryocrinites, there are two, Vasocrinns 

 and Barycrinus, in which both arms and cup are constructed 

 on the same essential plan as in Butryocrinus. When Messrs. 

 Wachsmuth and Springer last discussed these three genera* 

 they could point to more differences than would now be 

 possible, yet even then the differences were not very great. 

 We may proceed to discuss these differences in order. 



The Dorsal Cup in Botryociinus is cyathiforu), in Bary- 

 crinus and Vasocrinus it is shallow : its plates in Barycrinus 

 are massive and protuberant, in Vasocrinus thin, and in both 

 these genera axial folding is well marked ; in Botryocrinus 

 there is some variety in the protuberance and solidity of the 

 plates, while axial folding is seen in the course of develop- 

 ment. So far the differences are unimportant. 



The Arms in Barycrinus are robust^ in Vasocrinus less 

 robust ; in Botryocrinus they are either massive or graceful. 

 Ihe costals in Barycrinus are stated to be invariably 2 

 (Revision, p. 100), while Vasocrinus appears to have had 3 



* Eevision, I. (.96-100), Proc. 1879, pp. 319-323. 



