908 DR. F. A. BATHER ON 



was sliglitly bevelled so as to give this the appearance of a very 

 obtuse angle, with its apex about in the middle line of the radial. 

 This appears to represent a greatly simplified brachial facet, but 

 there are no articular markings, unless it be a slight depression 

 near the middle. 



The r. ant. R was similar in its general outline to the ant. and 

 1. ant. RR, having, like them, the basiradial suture longer on the 

 posterior than on the antei'ior side. It differs, however, in that 

 its left or posterior side is divided into two tracts : one a very 

 short suture connecting the upper angle of the plate with what 

 seems to be part of the r. post. R ; the other an excavate margin 

 to the peripi'oct. The curve of this margin throws the left upper 

 portion of the radial away from the median line, so that the sub- 

 angular concavity of the facet is longer on the left than on the 

 right. 



The r. post. R is probably represented partly by a small 

 fragment still attached to r. ant. R and partly by a fragment 

 attached to 1. post. R. The right-hand fragment has been pushed 

 slightly inwards. Whether these fragments all rejoresent the 

 r. post. R, whether a part or the whole may not represent anal or 

 perisomic plates, are questions that cannot be settled on the 

 evidence of this specimen. [Dr. Wanner in litt. confirms and 

 extends my observation of some small plate or plates in this 

 position, one of which, at any rate, he identifies with r. post. R.] 

 The really important fact is that r.post.R has been so far 

 atr'ophied that we may safely infer the entire absence of any 

 r.'post. arm. 



The 1. post. R is, in every direction, larger than the others. 

 It rests, almost symmetrically, on the shoulders of the 1. post, a.nd 

 post. BB and abuts normally on 1. ant. R. On its right {i. e. 

 posterior) side, however, the radial in its lower part bounds the 

 periproct, and in its upper part has a short sutural union with 

 the supposed r. post. R. The upper, or peristomial, margin is 

 regularly concave, with a slightly more marked curvature than 

 that of the other radials, but shows no bevelling, groove, or 

 depression, such as might suggest an articular facet. Outside 

 this margin, however, the highest part of the plate rises into a 

 mass of calcite (possibly stereom), which has been truncated by a 

 cleavage-fractui'e, sloping slightly downwards and outwards from 

 the oral pole. The evidence of the holotype leaves it uncertain 

 whether this protuberance formed the base of a mere hump, of an 

 unjointed spine, or of an arm ; but Dr. Wanner tells me that 

 some of his specimens permit " die sichere Beobachtung, dass 

 1. p. R eine Gelenkflache fur einen Ai^m zeigt," and his diagrams 

 show that this joint-face corresponds with the cleavage-surface 

 just described. It will be interesting to learn the exact consti- 

 tution of this facet, whether it has a fulcral ridge and axial canal, 

 and whether there is a ventral groove leading down to the 

 peristome. Of such structures the holotype pi^esents no trace 

 whatever. 



