912 DR. F. A. BATHER ON 



subglobular shape of tlie cup, the small diameter of the stem- facet, 

 the relatively large size of the infrabasals, which in the Flexibilia 

 are rarely visible, the rise of the I'adials towards their facets 

 curiously resembling the hump of the arm-bearing radial in 

 '•'Hy piriformis, the crowding of the facets I'ound the peristome 

 which thus becomes relatively small, and, finally, of greatest 

 interest in this connection, the outward projection of the posterior 

 basal, which, combined with the constriction of the upper part 

 of the cup, almost entirely separates the rectal channel from the 

 general thecal cavity. In the actual fossil the anal plates, which 

 once rested on the posterior basal, have been broken away, so 

 that the appearance is that of a periproct, opening at the top of 

 the posterior basal and at the lower corners of the adjacent 

 radials. 



Given, then, the existence of such a form in Middle Oar- 

 bonifei'ous times, it is easy to see how the accentuation of the 

 left posterior radial with its arm would have pushed the periproct 

 further to the right, and crowded out the right posterior radial. 

 This and the diminution of the other arms would have produced 

 a form agreeing with '■'■H." jiififormis. On this hypothesis some of 

 the minute plates between the left posterior and right anterior 

 radials may be relics of the perisomic plates. 



Physiologically considered, a modification bringing the food- 

 intake so close to the vent would be curious in any group of 

 crinoids ; but that such a modification would not be altogether 

 out of character with the Flexibilia may be gathered from a 

 perusal of two suggestive paragraphs by Dr. Springer (Journ. 

 Geol. vol. xiv. pp. 496, 497, 1906). Speaking of "that strange 

 influence which has modified the bilateral symmetry of almost 

 every genus in this entire group," he points out that " if the arms 

 have an asymmetrical distortion, it is to the right, never to the 

 left." If the anals are shifted, it is likewise to the right, so that 

 the excavation of the posterior basal for their reception is "on the 

 right shoulder of the plate." 



Timor is a long way from Britain, and I am not going to say 

 that the genus which must be established for "i7." piriformis is 

 necessarily descended from the genus to which our Yorkshire 

 fossil belongs ; but I do claim to have shown some reason for 

 thinking that " H." piriformis may belong to the Taxocrinidse, 

 and that, peculiarly modified though it is, its very modifications 

 are exaggerations of a tendency natural to that Family. 



Accepting this systematic position, at all events until it is 

 proved erroneous, we may draw up the following : — 



Generic Diagnosis. — A Taxocrinid with no radianal, with large 

 IBB forming a conspicuous part of the cup, with left post. R and 

 arm enlarged and all others reduced in size, the right post. R 

 being almost entirely atrophied, so that the rectum passes between 

 post, and r. post. BB below an<l 1. post, and r. ant. RR above. 



