1X)8 PALiEOZOIC ECHINODERMATA. 



Platycrinus diadema (M'Coy). 



Sp. Char. Body very much depressed, spheroidal (from the base 

 of pelvis to the vertex one-third less than the diameter between 

 the arms) ; pelvis large, depressed, pentagonal, without divi- 

 sional lines ; columnar adherence circular, crenated, one-third 

 the diameter of the pelvis, but seated in the bottom of a deep 

 circular excavation three-fourths the diameter of the pelvis ; 

 scapul<2 hexagonal, nearly twice as wide above as below, about 

 one-third wider than long, very slightly convex except at the 

 articulation for the arms, which are prominent, very large, 

 broad, and two-thirds the depth of the plate ; interscapular 

 plate large, hexagonal ; visceral plates rather small, hemisphe- 

 rical. Height from pelvis to vertex 1 inch. 



The very wide, depressed, turban-like form of this species 

 (which I find constant) easily distinguishes it from its congeners. 

 All the plates are even and smooth. 



Not uncommon in the white decomposing encrinal beds of 

 carboniferous limestone at Cleenish, co. Fermanagh, north of 

 Ireland. 



(Col. University of Cambridge and Royal Dublin Society.) 



Platycrinus megastylus (M^Coy). 



Sp. Char. Body broad ovate, visceral portion convex, not much 

 elevated; cup rapidly expanding, conical; pelvis pentagonal, 

 very small, resembling a prominent rim to the very large cir- 

 cular columnar attachment, the diameter of which is three 

 times greater than from its circumference to the edge of the 

 pelvic plate ; scapulcB slightly convex, even, nearly twice as wide 

 above as below, little wider than long ; excavations for the arm- 

 plates large, nearly half the depth of the scapulse ; capital plates 

 variable in size and number, but large, few, unequal, polygonal, 

 and most of them presenting a large conical protuberance in 

 the centre ; entire surface smooth. Length of body 10 lines, 

 width between the arras 9 lines. 



This species is excellently figured by Prof. Phillips (Geol. 

 Yorksh.) with a doubtful reference to the P. l(jevis of Miller. The 

 latter species is, I believe, generally admitted now to be distinct, 

 but having examined specimens agreeing with the above figure, 

 I find the species to which it belongs differs both from that to 

 which Goldfuss and that to which Mr. Austin have referred it, 

 by the comparatively enormous size of the columnar attachment, 

 and the narrow prominent rim to which the rest of the pelvic 

 plate seems reduced. 



The specimens above described are from the carboniferous 

 limestone of Bolland, where it occurs in company with numbers 



