Vol. 54.] 



MR. F. A. BATHER ON PETALOCRINUS. 



437 



interradially-situated plates, lead one to refer the genus to the 

 Sub- Order Cyathocrinoidea rather than to the Dendrocrinoidea. 



Among Cyathocrinoidea the family Cyathocrinidae is that which 

 has already been mentioned as presenting certain resemblances ; 

 but the apparent absence from the cup of an anal plate prevents us 

 from placing Petalocrinus actually within that family ; so far as 

 that is concerned, it agrees better with Codiacrinidse, which are 

 descendants of Cyathocrinidae. The peculiar structure of the arms 

 seems, however, to justify the erection of a separate family for 

 Petalocrinus, as was in fact proposed by the founders of the genus. 



Search must next bo made among Cyathocrinidae for a genus 

 from which Petalocrinus may have sprung. This appears to be 

 afforded by Gissoorinus, or still better by the subgenus Arachno- 

 crinus, which is the chief American representative of the genus 

 (text-fig. 15). The dorsal cup 



Pig. 15. — Arachnocrinus bulbosus. 

 Diagrams adapted from J. Hall^ 



of Arachnocrinus is rounded 

 and depressed ; the infrabasals, 

 which may be 3, as in the 

 normal Gissocrinus, are as 

 minute and as hard to dis- 

 tinguish as in Petalocrinus. 

 The radial facet is almost ver- 

 tical, and the arms come off at 

 right angles to the vertical axis 

 of the calyx, and continue in 

 that plane for some distance. 

 The same is the case with Gis- 

 socrinus incurvatus of Gotland, 

 which, though intimately con- 

 nected with undoubted Gisso- 

 crini, was in part doubtfully 

 referred to Arachnocrinus 

 by Wachsmuth & Springer, 

 whose action was discussed on 

 p. 168 of 'The Crinoidea of 

 Gotland: I.' 



The difficulty of the com- 

 parison with Arachnocrinus lies 

 in the lateral origin and hori- 

 zontal position of the anal tube 

 in that genus. I have tried to 

 convince myself that certain 

 elongate masses seen between 

 some arm-fans in one or two 



Fifteenth Rep. State Cab. Nat. 

 Hist. N.Y. pi. i,figs. 19, 20, 4^ 



21 {1862). 



(i) Basal view, with part of one arm 

 shown. B, basal circlet; R, radial 

 circlet ; x, anal ; 1-7. V, series of 

 brachials, (ii) View from left post. 

 radius, a small part of right post, arm 

 remains attached (iii) Yentral view 



'" of a portion of an arm, showing the 

 deep grooves and their bifurcation 

 within the axillaries, [ X ^--l 



specimens of Petalocrinus 



might represent fragments of a similarly placed anal tube, but 

 without success. Negative evidence, however, is not fatal to the 

 comparison, and we are not bound to postulate an anal tube in 

 every Arachtiocrinus or descendant thereof. A single species of 

 Cyathocrinus may have an anal tube in some individuals and a mere 



