Dr. F. A. Bather — A Ciinoid from the Red Crag. 207 



been closely anchylosed to one another and to the lower undivided 

 half of the fossil (Fig. 2). 



The upper face of the fossil, so far as its worn condition enables one 

 to judge, is flat towards the margin, but slightly excavate towai'ds the 

 centre, not so excavate as the lower end. The actual centre is occupied 

 bj' an axial canal, the borders of which appear to bear some radiating 

 grooves ; but these and the other markings of this face are so obscure 

 that it is safer to attempt no description. If vertical lines be drawn 

 upwards from the cusps, in the position of the traces of the vertical 

 sutures, those lines seem in three or four cases to end in slight 

 pustules or elevations. At the boundary of this face there are, 

 however, three or four larger prominences, each coinciding with the 

 middle of one of the five elements (Fig. 1). 



The structures described have now to be interpreted. The five 

 elements of the upper half cannot well be anything but basals or 

 radials. That they are radials seems to result from the following 

 considerations. Had they been basals, they would have shown some 

 traces of a hexagonal outline, whereas they are pentagonal with 

 flattened upper surfaces. Their size is more consistent with their 

 being radials, since there is a tendency to the reduction of basals in all 

 crinoids of Tertiary and later age. 



If we accept the five upper elements as radials, we have to enquire 

 what has happened to the basals. Are they fused into the single 

 element forming the lower half of the fossil, or have they been 

 overgrown by the radials and included in the interior of the cup, 

 or have they possibly atrophied out of existence ? I am inclined to 

 adopt the first of these three explanations. The question may be put 

 in another way: is the lower half of the fossil a proximale (i.e. a 

 persistent top columnal), or is it a fused basal circlet ? Now 

 a proximale, while it has a modified upper face, for the reception of 

 the elements it supports, generally has a lower face like the articular 

 faces of the succeeding columnals. In the present instance those 

 columnals arc not known to us ; but we do know enough about 

 crinoids in general to be aware that a joint-face with a smooth 

 regular concavity rarely has a pentagonal border of pustules. This 

 pentagonal border is more readily explained as the last trace of the 

 original pentamerism of the fused basal circlet. 



Taking then, as a working hypothesis, the view that this fossil 

 consists of a fused basal circlet supporting five closely united radials, 

 we have to consider its systematic position. 



Of the six families of recent crinoids recognized in the Treatise on 

 Zoology (vol. iii, London, 1900), the Pentacrinida3 may at once be set 

 aside by reason of their stem-articulation. 



The Bourgueticririidae occasionally have columnals that recall the 

 massive appearance and outline of this fossil ; but in such forms the 

 joint-face of the proximal columnals always has a distinct f ulcral ridge, 

 and the basals are distinct. The Upper Cretaceous Mesocrinus might 

 otherwise have been thought to show some resemblance. Rhkocrinus, 

 which still lives in the North Atlantic, is the only genus of the 

 family recorded from Tertiary rocks, but bears no great likeness to 

 this fossil. 



