THE CRINOID HYPOCRINUS. 911 



base, the small IB is usually anterior, as in Hypocrinus. A few 

 other positions for it have been recorded, but not, so far as I can 

 find, the same as it occupies here, unless it be in the little- 

 known Ampheristocrinus Hall (1881) from the Niagara group of 

 Indiana. 



The radial facets of the Gasterocomidse are of the horse-shoe 

 shape so common in Cyathocrinoidea. In "i7." piriformis the 

 facets are so greatly modified that it is perhaps unsafe to base con- 

 clusions on them. The arm-bearing facet seems to have occupied 

 almost the full width of the peristomial margin of the left pos- 

 terior radial in the holotype ; but the diagram Dr. Wanner has 

 sent me shows it as occupying about half the width. There is, 

 in the holotype at any rate, no trace of the axial canal. The 

 other facets are atro^Dhied, it is true, but such traces of them as 

 there ai-e seem to indicate a pre-existing facet as wide as the 

 radial rather than one of horse-shoe outline. Wide facets are, 

 of course, almost universal in the Flexibilia Impinnata, though 

 not confined to that group. 



If the reference of "i/." piriformis to the Flexibilia be taken 

 as a possible hypothesis, we have next to inquire whether in that 

 Order the periproct ever emerges below the summit of the radials. 

 I am unable to find that such an arrangement has ever been 

 described in any known genus, but that is no valid argument 

 against the possibility. Among Dicyclica Inadunata this peculiar 

 position first appeal's suddenly in the Devonian, and I have already 

 hinted at the possibility of its independent reappearance towards 

 the close of the Carboniferous. Why, then, should it not have 

 appeared with equal suddenness in some other group, especially 

 when the form displaying it is peculiarly specialized in other 

 respects ? 



Here, moreover, some actual corroboration of the hypothesis 

 is afforded by the fossil which impelled me to make this first- 

 hand examination of Hypocrinus. That is a small cup or patina 

 from the uppermost bed of the Yoredale series, in Nidderdale, 

 Yorkshire. On it is based the new genus and species Cydono- 

 crinus p(i7'vidus (Bather, Oct, 1913). 



Cydonocrinus belongs to that group of Flexibilia in which, to 

 use Dr. Springer's words, "the rays and their divisions are 

 rounded exteriorly, and the interbrachial spaces relatively de- 

 pressed " (Journ. Geol. vol. xiv. p. 510, Oct. 1906). This character 

 aflects also the anal plates, which are " not united by suture with 

 adjacent rays, but in arm-like series, more or less separated from 

 them by perisome " (Spi-inger, op. cit. p. 519). Such forms con- 

 stitute the Taxocrinidee as defined by Dr. Springer, and it is clear 

 that, of the included genera, Cydonocrinus is most nearly allied 

 to Taxocrinus. Thus it has the same fundamental plan of the 

 cup as has '•'■Jiy piriformis. 



Now the features in which Cydonocrinus differs from Taxo- 

 crinus all bring it nearer to "i7." p>iriformis. They are the 



61* 



