112 PALEOZOIC ECHINODERMATA. 



the depressed, triangular intervening spaces are marked with 

 coarse, rough parallel strise nearly coinciding in direction with 

 the pseudambulacral ridges, and converging to the second set 

 of ridges ; the impressed lines between these strise seem punc- 

 tured, the fifth (? posterior) space is without sulcation. 



These strange and beautiful forms, the ^bell-stars,' as they 

 may be called, are obviously allied to Pentremites (taking P. Der- 

 biensis, florealis, oblongus, ellipticus, and such like as the types of 

 the genus), from which they differ in having the small basal 

 plates enormously developed into a conical pelvis, and having the 

 pseudambulacra entirely confined to the capital plates (which here 

 form a truncated disc) instead of being continued through a 

 slit in the supra-basal plates nearly to their base. On the nature 

 of the peculiar sulcation, represented in the subjoined sketch in 

 four of the interambulacral spaces, I have no remark to offer. In 

 Prof. Forbes^s paper on the British Cystidea in the second volume 

 of the ' Memoirs of the Geol. Survey,' p. 529, there is a figure 

 representing ^^ the projection of the arm-bearing surface of the 

 Pentremites pentagonalis" which resembles the disc of our genus 

 except in having the posterior interambulacral space sulcated, and 

 with a thick mesial ridge like the rest ; I do not suppose that that 

 figure is meant to represent the Platycrinus pentagonalis of Mil- 

 ler, forming the Pentremites id. of G. Sowerby and Phillips, which 

 presents no resemblance of the kind. I only know the following 

 two species, from the carboniferous limestone. 



Codaster acutus (M^Coy). 

 Sp. Char. Pelvic and supra-basal plates of equal length ; pelvis 

 acutely conical, obtusely subtrigonal in section ; columnar ad- 

 herence small, round, prominent; surface smooth. Length 

 6 lines, width of disc 5 lines. 



Not very uncommon in the carboniferous limestone of Bolland. 

 {Col. University of Cambridge.) 



Codaster trilohatus (M^Coy). 

 Sp. Char. Supra-basal one-third longer than the basal or pelvic 

 plates ; pelvis divided into three tumid lobes which hang be- 

 low the columnar adherence ; surface smooth. Length 7 lines, 

 width of disc 5 lines. 



Not uncommon in the carboniferous limestone of Derbyshire. 

 {Col, University of Cambridge.) 



Ord. Perischoechinida (M'Coy). 



All the known Echinida — from the spheroidal Echini with the 

 mouth and anus both central, one vertically under the other, to the 

 elongated, symmetrical Spatangi with their mouth and anus at 



i 



