344 ECHINOBRISSUS 



disc and other interesting details. One of these urchins (fig. 2/, g) enabled me to exhibit 

 a conoidal variety which sometimes occurs, but it would require many figures to do full 

 justice to all the variations of outline observed in the Northamptonshire specimens; 

 which hkewise exhibit the sculpture on the plates much better than those from Yorkshire. 

 The Gloucestershire specimens are rarely well preserved. This species is exceedingly rare 

 in the Wiltshire Cornbrash, which contains in such abundance B. chnicularis, Lhwyd. 



M. Triger collected E. orbicularis from the Forest Marble, Ass. No. 4, department of 

 the Sarthe, at Pecheseul, Noyen, route de Mamers a Montagne, where it is very rare. 

 I know of no other foreign locality in which it has been found. 



EcHiNOBRissus GUADEATUs, WfigJit, nov. sp. PI. XXVI, fig. 1 a, b, c, d. 



Test quadrate, elongated, depressed, narrow before, wide behind ; posterior border 

 deeply sulcated ; anal valley short, wide, and with sloping sides, extending to the apical disc, 

 which is excentral and nearer the posterior border ; dorsal surface much inclined from the 

 apical disc to the anterior border ; sides narrow ; base very concave ; plates of the test 

 closely covered with small tubercles. 



Dimensions. — Height, seven tenths of an inch ; antero-posterior diameter, one inch and 

 nine twentieths ; transverse diameter, one inch and three tenths of an inch. 



Description. — This nucleolite has by some been considered to represent Nmleolites 

 major, Agass., in the English Oolitic rocks, but a careful examination of M. Agassiz's 

 figure, given in the ' Echinodermes Fossiles de la Suisse,^ will convince the inquirer that 

 this urchin is very distinct from the Swiss form ; in our nucleolite the apical disc is 

 excentral, and situated nearer the posterior border, whereas in U, major the excentral disc 

 is nearer the anterior border ; the mouth-opening in our nucleolite is small and nearly 

 circular, whilst in E. major it is pentagonal, and much nearer the anterior border. Besides 

 these organic distinctions, they belong to widely different stages of the Oolitic rocks, B. 

 quadratus, Wright, being found in the Cornbrash, whereas B. major, Agas., was collected 

 from the " terrain Portlandien de la Vallee de la Birse." 



B. quadratusxs, a large, elongated nucleolite, with a well-defined quadrate outline, much 

 wider behind than before ; the upper surface is flat, and the slope from the disc to the anterior 

 border is long and gently declined ; the ambulacral areas are nearly all of the same width, and 

 terminate at a short distance from the apical disc, (fig. 1 a) ; they pass entirely straight 

 from the border to the disc, without forming curves as in B. clunicularis, Lhwyd. 



The poriferous zones are narrow; the pores forming the external row are only a 

 little larger than those of the inner row (fig. 1 d), and there are seven pairs of pores opposite 

 each large plate ; the inter-ambulacral areas are of" unequal width, the anterior pair are 



