﻿402 



PYGURUS 



base they are still larger, arid their deep areolas form hexagonal cells on different portions 

 of the base. 



Affinities and differences. — In its general characters, but more especially in the oblique, 

 tumid, conoidal elevation of the anterior half of its upper surface, Pygurus BlumenbacMi, 

 Koch, resembles three other congeneric forms — Pygurus Montmollini, Ag., P. Urbignianus, 

 Cott., and P. Bogerianus, Cott., from each of which it is distinguished, however, by specific 

 characters ; the first and second are Neocomian, and the latter Kimmeridge species. It 

 differs, according to M. Cotteau, from Pygurus Montmollini, Ag., in its greater size, less 

 elevated upper surface, and more rostrated posterior border. It differs from Pygurus 

 Orbignianus, Cott.,* equally by its size, by its less conical upper surface and more tumid 

 anterior border, by its petalloid ambulacra being more slender, by its inter-ambulacral 

 tubercles being closer together and more irregularly disposed. Pygurus Bogerianus, Cott.,t 

 more closely resembles P. Blumenbachii, but it appears to M. Cotteau, who has carefully 

 compared these two species, that P. Bogerianus is distinguished from the latter by the test 

 being much longer than it is wide, by the upper surface being more depressed, its 

 tubercles being less numerous, and its intermediate granules disposed in regular and 

 concentric series. 



The only two English specimens of this urchin which I know are those figured in our 

 plate ; the largest belongs to the Museum of Practical Geology, and was collected by the 

 officers of the Geological Survey ; the other is in my cabinet. These Pyguri are much 

 smaller than the very fine specimens which my friend M. Cotteau has so well figured 

 and described in his work, hence the comparison which he has made was between these 

 fine large specimens and the other species above enumerated, and which all belong to the 

 secondary rocks of France. M. Cotteau's specimen measures in height 34 millimetres = one 

 inch and nine twentieths ; antero-posterior diameter, 87 millimetres r= nearly three inches 

 and a half; and transverse diameter, 86 millimetres = three inches and four tenths. 



Locality and Stratigraphical position. — The specimen collected by the officers of the 

 Geological Survey was obtained from the Coral Rag at Abbotsbury, Dorsetshire, where it 

 is extremely rare. My specimen was said to have been procured from the Inferior Oolite, 

 near Yeovil, but this I have discovered to be a mistake. I have reason to believe that it 

 was collected from the Lower Calcareous Grit at Bullington Green, near Oxford, asso- 

 ciated with Cidaris Smithii, Wr., and Echinobrissus scutatus, Lamk. 



The foreign distribution of this species is as follows : In France it characterises the 

 inferior and superior stages of the Corallien. M. Cotteau collected it in " Calcaire blancs 



* 'Catalogue raisonne des Echinides du Terrain Neocomien,' p. 12. 



t " Note sur les Echinides de l'etage Kimmeridgien de l'Aube," ' Bull., de Geol. Soc. de France,' 2 e serie, 

 t. xi, p. 35C. 



X ' -Etudes sur les Echinides Fossiles du departemeut de 1'Yoiine,' p. 238. 



