308 Dr. T. Wright on the Cassidulida of the Oolites. 



Affinities and differences. — This large species resembles N. 

 Agassizii in size and outline, but is clearly distinguished from it 

 by the flatness of the dorsal surface, the length and narrowness 

 of the anal valley, and the absence of the undepressed portion of 

 test which is so conspicuous in N. Agassizii. It resembles N. 

 Solodurinus in the form and length of the anal valley, but differs 

 from it in having an orbicular circumference, and in the absence 

 of the produced, deflected, and truncated posterior border so cha- 

 racteristic of that species ; from N. Hugii it is distinguished by 

 the extension of the anal valley from the disc to the border, and 

 the inconsiderable deflection of the single interambulacral area. 

 After a careful examination of an extensive suite of specimens 

 from the Inferior Oolite and Great Oolite, we have come to the 

 conclusion that C. patella, Ag., and C. excentricus, M^Coy, are 

 not distinct species, but merely varieties of N. sinuatus ; as we 

 have before us a series exhibiting the forms which M. Agassiz 

 and Prof. M'Coy have considered as specifically distinct, with the 

 intermediate forms through which they blend into the true typical 

 N. sinuatus. Without several individuals from different localities, 

 it is at all times hazardous to attempt to establish a new species 

 of Urchin on form alone, as the same species often changes its 

 form in different beds and even in the same bed in different loca- 

 lities; these modifications of form constitute at most varieties, 

 which depended upon some temporary change of the conditions 

 in which they lived, without in any way affecting the distinctive 

 structural character of the species. 



Locality and stratigraphical ran^e. — N. sinuatus has a wide 

 vertical range, being found very abundantly, and of its largest 

 size, in the upper beds of the Inferior Oolite of Gloucestershire, 

 in the Great Oolite of Minchinhampton, and Kiddington (Oxon), 

 and the Cornbrash and Coralline Oolite of Wilts ; in Yorkshire 

 it is found in beds of the same ages. According to Agassiz and 

 Desor the foreign distribution of this species is, *' Inferior Oolite, 

 Boulogne-sur-mer ; Chayul (Ardennes) ; Montanville, Flincy 

 (Meuse) ; Metz, Noviant, Besan9on, Porrentruy, Salins (Jura) ; 

 environs de Bale.^^ 



History. — This species, as the synonyms prove, has been long 

 known to naturalists j it is so abundant in some localities in Glou- 

 cestershire, that the farmers believe this Urchin grows in the 

 soil, from the numbers that are successively turned up by the 

 plough every year. 



Nucleolites Agassizii, Wright, n. sp. PI. III. fig. 3 a-c. 



Test conoidal, with a nearly circular margin ; ambulacral arese 

 depressed, concave and petaloid, anterior pair much inclined ; 



