364 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [A.pril 22, 



which are the property of R. S. Cooper, Esq., of Bilston, while the 

 third belongs to the Manchester Museum. The last-mentioned is 

 the most perfect, and may therefore be conveniently described first, 

 as No. 1 (PL XIII. fig. 1). 



It was obtained from the coal-shales at Medlock Park Bridge, 

 and consists of an ironstone-nodule split into two pieces, a larger 

 and a smaller. The face of the latter exhibits a relief of the fossil, 

 while the opposed surface of the larger piece presents the corre- 

 sponding cast. Exclusive of the appendages, what we may call the 

 body of the fossil (fig. 1 a) measures about 1^ inch in length, and 

 has a width of ratheV more than |^ths of an inch at its widest part. 



The one end of the body (fig. 1 b, c) is much broader than the 

 other, and has the form of a semicircular disk, the base of the semi- 

 circle forming the widest part of the body, and being about half an 

 inch distant from the summit of its curve. 



The opposite end has the appearance of a quadrate disk («), about 

 -f-^ inch long ; and between this quadrate disk and the semicircular 

 disk just described lies the central portion of the body (b) divided 

 into a series of segments. Two pairs of appendages, one large (2') 

 and one small (1'), are attached to the extremity of the quadrate 

 disk, while a number of slender limbs are connected with the sides 

 of the segmented part of the body, the four pairs nearer the quadrate 

 disk being directed towards that end of the body, while the others 

 pass more directly outwards. 



The semicircular disk (c) is traversed by a strong transverse de- 

 pression about the middle of its length, which divides it into a wide 

 proximal, and a narrower distal portion. The latter is convex in the 

 direction of the long axis of the body, and presents a little tubercle 

 on each side of the median line close to the transverse depression. 

 The periphery of the distal portion has the form of a curved ridge, 

 separated by a corresponding groove from the rest of the upper sur- 

 face, and by another groove from the line of junction of the upper 

 and lower surfaces (g). On clearing away the matrix as far as was 

 practicable, I found the under surface of this part to be far more 

 convex than the upper, and to present a transverse line apparently 

 indicating the boundary of a segment. In consequence of its con- 

 vexity inferiorly, this portion of the body has a thickness of as 

 much as |^ths of an inch. 



The proximal portion of the semicircular disk appears to be some- 

 what crushed ; it is divided by two well-marked longitudinal depres- 

 sions, which converge from the ends of the transverse depression 

 into a central lobe, narrower proximally than distally, and two lateral 

 ones, whose wider extremities are turned in the opposite direction. 



The proximal half of the quadrate disk («) presents two convex 

 lateral eminences, separated by a slight depression, which, like the 

 distal half, is obscured by portions of the matrix. The larger 

 lateral appendage (2', 2") attached to the distal half, is, on the right 

 side, composed of a short, wide, basal articulation, with which a 

 quadrate joint, produced into a spine at its outer and distal angle, and 

 presenting a convex outer curve, is articulated. Apparently con- 



