﻿FROM THE UPPER GREENSAND. 



239 



convex above, inflated at the sides and flattened below; vent large, supra-marginal, 

 elliptical ; mouth-opening central, opposite the disc ; tubercles small, surface of the plates 

 smooth. 



Dimensions. — Anterior posterior diameter eleven twentieths of an inch ; height seven 

 twentieths of an inch. 



Description. — This little Urchin appears to be a very rare form, as the example before 

 me is the only specimen I have seen in English collections ; the type specimen figured by 

 my friend Professor Desor, in his Monograph on the Galerites belonged to M. 

 Deshayes and was the only one known to him. 



M. Cotteau has not seen the original, giving copies of Prof. Desor's figure of the test 

 and quoting his description of its structure in his ' Paleontologie Francaise.' My 

 specimen was collected several years ago from the Upper Greensand near Chute farm, 

 Wilts, along with some fine examples of Catopygus columbarius and Cottaldia Benettice, 

 so that there is no doubt of the horizon of the English specimen. The general outline 

 of the test is indistinctly pentagonal, enlarged before and slightly narrower behind (fig. 1 b 

 and fig. 1 c). The upper surface is convex, the sides inflated, and the base flat (fig. 1 a ; 

 fig. 1 e) ; its height is about one half the length of the test. The plates are covered with 

 small tubercles, which are very indistinctly seen ; those at the base are larger. The vent 

 occupies the middle of the border ; the periprocte is large, of an elliptical shape, and 

 placed a little nearer to the base than the upper surface. The sur-anal carina is only 

 slightly developed around the lower part of periprocte. The lower surface is nearly flat, 

 with the margin round, and the small mouth-opening is situated in the middle of the 

 base directly opposite the vertex. 



Affinities and Differences. — This species is readily distinguished from Pyrina 

 Desmoulinsii by its sub-pentagonal form enlarged before and contracted behind; its 

 sides are likewise more inflated and the lower angle of the periprocte is nearest the base, 

 Avhilst in P. Desmoulinsii the upper angle of that aperture is nearest the dorsal surface. 



Locality and Stratigraphical Position. — I collected this Urchin from the Upper 

 Greensand of Chute Farm, near Wilts, with Catopygus columbarius, Cottaldia Benettice, 

 and other well-known forms of Urchins and Mollusca belonging to that stratum. 



The type figured by M. Desor was obtained from the Cretaceous rocks of France, and 

 as it was communicated to M. Desor by M. Deshayes without the indication of the forma- 

 tion from whence it was collected, we are unfortunately in ignorance of its stratigraphical 

 position, and as M. Cotteau had not seen the specimen, he was unable to give an opinion 

 on the matrix. 



