DESCRIPTIONS OP PHB SPECIES. 293 



<mly just reaching the deltoid plates al their proximal ends. Hydrospirc-folds six to 

 eight in number ; the tubes short and curving inwards. Mouth small. Anus at the 

 proximal end of the posterior deltoid. Column circular; canal large. Ornament 

 seldom preserved, but when so the striae are fine and regular, and usually well marked 

 on the outwardly bevelled margins of the radial sinuses. 



Remarks. Orophocrinus pentangtdaris was originally described by Miller as a 

 Platycrinus, but, according to Mr. G. B. Sowerby, arms were added to one of his 

 figures to increase the resemblance to this generic type ! ' Notwithstanding this, 

 Miller's other figure and description are a clear interpretation of the species meant, 

 and therefore Cumberland's more accurately defined but later name cannot be adopted. 

 Platycrinites pcntangularis, Miller, sp., also formed the type of d'Orbigny's genus 

 Limorplticrinus, which, however, has never been adopted by palaeontologists on 

 account of the erroneous and incomplete nature of his generic diagnosis. 



The radial plates of 0. pentangularis are each marked by four impressed lines 

 radiating from the lips to the basiradial sutures. Two of these are almost in the 

 middle line, and bound the obtusely convex central portions of the plates, whilst the 

 other two pass to the lateral angles. The edges of the radials are bevelled outwards 

 along the sinuses, and the resulting surfaces are marked with cross stria?. On the 

 two limbs forming the anal interradius the bevelled portions are wider and more 

 pronounced, while the cross stria? are stronger. 



We have carefully studied the unique specimen of Pentremites Waterhousianus, 

 de Kon. and le Hon (PI. XV. figs. S-10 ; PI. XVI. figs. 8, 9), and we regret that we 

 cannot agree with these eminent writers in regarding it as distinct from Miller's 

 species. The specimen, so far as the summit characters are concerned, is in a 

 better state of preservation than the generality of British Blastoids, but the structure 

 of the parts is identical with that of O. pentangularis, even including the ornament 

 of the calyx. The base of the Belgian fossil, on the other hand, was clearly injured 

 and partially distorted during the life of the Blastoid, as indeed its describers pointed 

 out. The reparation of this injury seems to have been accompanied by the growth 

 of extra plates around the base, and the partial covering of these plates with a 

 secondary deposit of calcareous matter, so as to give a spurious ornamentation to 

 the lower portion of the cup. 



Orophocrinus pcntangularis may be distinguished from 0. stelliformis, 0. gracilis, 

 and 0. vents by the increased height of the calyx between the columnar articulation 

 and the radial lips, by its shorter ambulacra and depressed summit, and by its wide 

 and long hydrospire-clefts. It does not appear to be a common species, judging 

 from the small number of examples that we have met with. Good sections 

 for the microscope are difficult to obtain, and our figure of the hydrospires 



1 Zool. Journ. 1 834, vol. v. no. 20, p. 457. 



