﻿FROM THE CORALLINE OOLITE. 



395 



Pygurus pentagonalis, Phil. PI. XXXVI, fig. 1 a, b, c, dj fig. 2 a, b. 



Echinanthixes orbicularis. Young and Bird, Geol. Surv. of Yorksh. Coast, pi. vi, fig. 5, 



p. 213, 1822. 



Clypeaster pentagonalis. Phillips, Geology of Yorkshire, pi. iv, fig. 24, 1S29. 

 Echinolampas pentagonalis. Morris, Catalogue of British Fossils, p. 52, 1843. 

 Pygurus pentagonalis. Forbes, in Morris's Catalogue of Brit. Fossils, 2d ed.p.8, 1854. 



— — Desor, Synopsis des Echinides Fossiles, p. 314, 1858. 



Test sub-pentagonal, emarginate, and concave anteriorly, wide in the middle, produced, 

 and deflected posteriorly ; upper surface convex, with a conical vertex, ambulacral areas 

 and poriferous zones widely petalloid in the upper two thirds of the dorsal surface, and very 

 narrow in the lower third ; apical disc small, central, forming the vertex of the test ; under 

 surface concave ; basal inter-ambulacral cushions moderately prominent ; mouth-opening 

 small, sub-central, forwards ; peristome pentagonal, with five mammillated oral lobes and 

 five narrow ambulacral phylloidal floscules ; vent elliptical, infra-marginal, situated in a 

 deep anal valley. 



Dimensions. — a. Height, one inch and four tenths ; transverse diameter, three inches 

 and three quarters ; antero-posterior diameter, three inches and nine tenths. 



b. Transverse diameter, three inches and a half ; antero-posterior diameter, three inches 

 and four tenths. 



c. Height, one inch and one fifth ; transverse diameter, three inches ; antero-posterior 

 diameter, three inches. 



Description. — I have given the measurements of three different Yorkshire specimens of 

 this Pygurus. The specimen a was collected from the Coralline Oolite at Hildenley, near 

 Malton, by C. W. Strickland, Esq. ; the specimen b was obtained near Scarborough, 

 and belongs to the Scarborough Museum ; and the specimen c was collected from the 

 Lower Calcareous Grit near Scarborough. The examples from the Coralline Oolite are in 

 general much larger than those found in the Lower Calcareous Grit. 



The test has an orbicular or sub-pentagonal form ; the anterior border is emarginate and 

 concave ; the antero-lateral border expands outwards to the middle of the test, where its 

 greatest diameter is attained. The postero-lateral border slopes inwards and backwards, 

 and forms a rostrated and deflected termination. This is the form of the urchin figured 

 in fig. 1 a, b, from the Calcareous Grit, which may be taken as a type of the species. 

 In the one from the Coralline Oolite (fig. 2 a) the test is altogether orbicular, and more 

 convex. 



The ambulacral areas are remarkably petalloid (fig. 1 a) on the upper surface, the lower 

 third of the area is very narrow, the middle third much expanded, and the upper third 



