Di:s( iniTioxs of Tin: si'iX'iKs. 249 



Pentremites orbicularis, Rofe, Geol. Mag. L865, vol. ii. p. 249. 



Granatocrinus orbicularis, E. & ('., Ann. & Mag. Nat. Hist. 1882, vol. ix. p. 2.'3'J. 



Sp. Char. Calyx globose ; summit converging, concave ; base somewhat contracted 

 and faintly concave ; section almost round, or very slightly decagonal, sometimes with 

 almost Hat sides; periphery nearly equatorial. Basal plates quite concealed; basi- 

 radial sutures confined to the central cavity. Radial plates pentagonal, more than 

 half as long as the calyx, nearly flat-sided, and widening rapidly upwards; bodies 

 remarkably small, concave, and so assisting to form the basal concavity; limbs long 

 and broad, obliquely truncated above; sinuses very narrow, and sublinear, parallel- 

 sided ; radio-deltoid sutures forming a wide and open angle. Deltoid plates very 

 large, broadly rhombic, with small depressed and constricted apices, all but the anal 

 one bearing a node or prominence behind the spiracle. Ambulacra very narrow, 

 projecting slightly above the edges of the sinuses; median grooves of the lancet- 

 plates exposed between half and two thirds the length of the ambulacra; side plates 

 very numerous, comma-shaped ; outer side plates curved, and excavated for the pores, 

 which are more or less triangular. One hydrospire-tube on each side of an ambula- 

 crum ; their sacs almost circular in section. Spiracles small, triangular-pyriform, 

 opening inwards and obliquely upwards; anal spiracle much larger than the others. 

 Ornament of very minute granules arranged in lines parallel to the margins of the 

 plates, with a stronger series bordering the edges of the sinuses. 



Bemarks. G. orbicularis appears to be a tolerably abundant species in certain 

 localities, and may be readily recognized by its orbicular or globose outline and 

 large deltoid plates. It may be distinguished from G. Derbiensis by the position of 

 the radio-deltoid sutures, which in G. orbicularis are above the equator (PI. IX. 

 figs. 11, 12), whilst in the latter species they are near the base (figs. 1-1, G). Except 

 as regards these sutures, the resemblance between these two species is a close one. 

 In G. campanulatus the base is broad and flat (PI. VIII. fig. 13), and although the 

 radio-deltoid sutures occupy nearly the same position the angle which they form is a 

 very different one (fig. 11), and the height of the calyx, as compared with its breadth, 

 bears no relation to the same measurements in G. orbicularis. 



The ambulacral pores of the latter type are enclosed between the margins of the 

 radials, the lower margins of the side plates above, and the upper oblique margins of 

 the outer side plates below, and are, roughly speaking, triangular in shape (PL IX. 

 fig. 16). 



We have had the advantage of studying the specimen which was figured both by 

 Mr. G. 13. Sowerby and by Prof. John Phillips. There is a considerable variation 

 both in the general shape of the calyx (PI. IX. figs. 11, 12), and in the capacity of 

 the peristome (figs. 11, 15). 



Localities and Horizon. Bolland District, Lancashire ; Clitheroe, Lancashire (Pre- 

 sented by the late J. Rofe, Esq., F.G.S.) : Carboniferous Limestone. 



2k 



