Mr. F. M‘Coy on some new Paleozoic Echinodermata. 251 
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 im 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 athick mesial ridge like the rest ; 1 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 trilobatus (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 dise 5 lines. 
Not uncommon in the carboniferous limestone of Derbyshire. 
(Col. ee of Cambridge.) 
Ord. PeriscHorcuinipa (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 
opposite ends of the ventral disc—all agree in having their case 
made up of twenty vertical rows of plates, ten ambulacral and ten 
interambulacral. This is not only the most persistent character 
of the entire group, but the number becomes of extreme interest 
when, with Agassiz and Valentin, we view the globose test of the 
sea-urchins as a mere modification of the same parts which we find 
in a 5-rayed starfish,—an ideal division of the mesial suture con- 
necting the two rows of plates in each interambulacrum of the 
former, giving at once the ambulacra, lateral ossicles, and other 
characters of the latter. The Echinites of the palzeozoic rocks 
however are constructed on an entirely different plan, having three 
