﻿FROM THE CHLORITIC MARL. 



237 



The vent is elliptical, and placed in the middle of the posterior border (fig. 2 d), 

 ■nearer the upper than the under surface (fig. 2 a). 



The apical disc is small, and composed of four ovarial plates, of which the right 

 antero-lateral is much the largest, and supports a spongy madreporiform body. All these 

 plates are perforated (fig. 2/). The ocular plates, five in number, are small, and well 

 wedged in between the ovarials. 



Affinities and Differences. — The regular elliptical elongated form of Pyrina Desmou- 

 linsii, with its flattened upper surface and pulvinated base, distinguish this species from 

 its congeners. I have compared specimens obtained from the Etage Cenomanien of the 

 environs of Tournay, Belgium, with specimens collected from the Chloritic Marl at 

 Chard, and find them to be identical in all their details. It very much resembles Pyrina 

 ovulum, which, however, is a smaller form, with a more inflated test, and the elliptical 

 vent is situated near the dorsum. Compare fig. 2 and fig. 3, where the affinities and 

 differences are well shown in the admirable figures in PL LIV. 



It differs from Pyrina lavis in having a narrower test of a more regular elliptical 

 figure, and wants the inflation of the anterior portion and the tapering of its posterior 

 border. 



Locality and StratigrapMcal Position. — This rare Urchin was collected by Mr. Weistj 

 in the Chloritic Marl, near Chard, and Mr. Pratt obtained another from the same locality 

 and stratum, which has been beautifully figured in the ' Memoirs of the Geological 

 Survey,' Decade v, pi. vi. The short description was from the pen of my old 

 esteemed friend Dr. Woodward, to whom I forwarded all my materials when he was 

 engaged in writing the text for the description of pi. vi of that Decade. 



Pyrina ovulum, Lamarck, sp. PI. LIV, fig. 3 a — h. 



■ r 



Nucleolites ovulum, Lamarck. Anim. sans vert., t. iii, p. 37, 1816. 



— — Deslong champs. Encycl. Method., t. ii, p. 500, 1824. 



— — Defiance. Die. des Sc. Nat., t. xxxv, p. 213, 1825. 

 Pyrina — Agassiz. Cat. Syst., p. 7, 1840. 



Nucleolites — Besor. Mon. des Galerites, p. 26, pi. v, figs. 35 — 37, 1842. 



— — Agassiz et Desor. Cat. rais. des Echinides, p. 92, 1842. 



— — oVOrbigny. Prodrome, t. ii, p. 271, 1847. 



_ _ Morris. Catal. of British Fossils, 2 ed, p. 88, 1854. 



— — Woodward. Mem. Geol. Surv., Decade v, pi. vi, 1856. 



_ _ Cotteau. Paleontologie Franchise, pi. 985, figs. 7—11, tome 



vi, p. 484, 1855. 



