CONTRIBUTIONS TO PAL.EONTOLOGT. 85 



feet in some of its parts. The specimen gives no indication of having grown 

 in any other form than a circular, slightly concave disc. The centre, point of 

 attachment, or stem, is unknown. It is an impression in the stone, consist- 

 ing of radiating and concentric bands. The rays, near their origin, are less 

 than a line in width, and, at the distance of six inches, are a little more than 

 a quarter of an inch in width ; some of them gradually narrowing towards 

 their outer extremity. They are not striated or marked in any manner, the 

 edges of the impressions being slightly raised. The concentric bands are 

 simple and continuous, not striated or otherwise marked, and are slightly 

 raised at the margins. Those near the origin of the rays are less than a line 

 in width, and each successive one becomes a little wider ; so that the outer 

 ones have about the same width as the rays in their widest part. The rays 

 are not equidistant, and some of them show a slight curvature throughout 

 nearly their entire extent. In the portion of the disc preserved there are 

 nine rays and the marks of twenty concentric bands, and there were pro- 

 bably two or three more between the inner one and the centre. The inter- 

 spaces between these parallel bands and the rays are sharply quadrangular, 

 being of the same width or wider than the bands near the centre, becoming 

 proportionally less until near the margin, when they are not more than half 

 the width of the parallel bands. In the lateral direction, the spaces increase 

 rapidly on receding from the centre. 



This specimen has an unusual and very artificial appearance. The regular 

 flat bands essentially parallel with each other, with similar radiating bands, 

 mark the limits of the organic substance; while there are regular interspaces 

 where there is no organic marking, showing the want of continuity in the 

 investing substance. All this renders it difficult to give any plausible ex- 

 planation of its mode of growth. It is possible that the apparently parallel 

 bands are a continuous spiral band ; but there is no evidence of this in the 

 fragment, nor can it be positively asserted that the entire form was circular: 

 it may have been broadly flabelliform, with a stem or footstalk. 



The most remarkable feature is the want of continuity in the frond, since 

 both the radiating and parallel bands are distinctly limited, showing no 

 evidence whatever of any organic substance or marking in the intervals. 

 In this respect, all the other forms which I have seen, and with which this 

 may be regarded as allied, differ in a conspicuous manner. In the specimen 

 fig. 2, Plate iv, we have a cast of the interior of a funnel-shaped frond, 

 which is sharply striated both radiatingly and concentrically ; but there 

 are no interspaces which do not bear evidence of organic impressions. 



In fig. 1, which I regard as the exterior of the same species, the substance 

 of the frond is everywhere continuous, and the stronger radii do not appear 

 to be so conspicuous on the exterior as upon the interior. In the surface- 

 markings of fig. 2 we have a close similarity with the surface of the origi- 

 nal of Hydnoceras, and the analogy is farther confirmed by intermediate 

 forms illustrated on Plates iv, v & V A. 



