252 Mr. F. A. Bather on 



latter ; and tliis carries Avith it, first the boundiiifj,' of tlie 

 periproct by tliat radial, instead of by a reduced right 

 posterior radial and the adjoining right anterior radial ; 

 secondly the position of the periproct in the middle line of 

 the posterior basal, instead of at the adjacent upper corners 

 ot the posterior and right posterior basals. 



There are, however, distinct modifications from a normally 

 symmetrical crinoid. The whole cup is raised along the left 

 posterior radius, and depressed towards the opposite side, 

 and this position was accentuated by the slo[)e of the stem- 

 facet. The asymmetry of the radial region is shown in 

 Austin's reeonstructiou (PI. X. fig. 2e), but the slope of 

 the stem-facet is not shown and would be inconsistent with 

 such a stem and general habitus as are re])resented in that 

 drawing. 



Further, there seems good reason to sup])ose that the arm 

 borne by the left posterior radial Was relatively stout, but 

 that the other arms were much reducedi, and possibly 

 modified into flattened plates serving more for protection of 

 the peristome than for the collection of food (PI. X. 

 fig. 1^/). Austin's reconstruction is certainly incorrect in 

 showing five small arms of equal size. 



The general shape of the jjostcrior basal is like that in 

 Cyloaocrhius (Ann. & iMag. >s'at. FIist.,Nov. 1913, p. 3H8), 

 but the periproct was definitely closed above by the union of 

 the radials, with or without a small intercalated plate. There 

 is no reason to doubt the eorrectnessof Austin's representation 

 of a small anal tube projecting outwards from the pcri[)roct 

 (PI. X. Hg. 2Z»). 



In all these modified Ceaturos, Si/cocrinus aiwpeptamcnm \s 

 much nearer to '^ Hi/potriiius" pirifomiis than to such a 

 form as Cydunocrinus, and it may indeed be questioned 

 Avhether the two species should be separated generically. 

 Apart from diflerence of size, the only distinction lies in the 

 slight intensification of all the above-mentioned features in 

 " II." ijirifonn'is. 



The Systematic Conclusions to which we are led seem to be 

 these. Sijcocrii.us was described by the Austins in terms 

 that were intelligii)le emmgh to contemporary writers, as 

 ])roved by the remarks of XOn Huch. Our analysis of their 

 definitions has, however, brought out rather more ch^arly 

 the fact that at least two (|uite distin(;t i)lans ol" structure — 

 the monocyclic and the dicyclie l)ase — were confused l)y 

 them. The dicyclie plan seems to be that most in accord 

 with the intention of the generic diagnosis, and we niay 



