from the Lius and Oolites. 167 



only three pairs of primary tubercles in the interambulacral areas, 

 those of the base being closely set together, and those on the 

 sides at gi-eat distances apart ; the tubercles are large and hemi- 

 spherical and only slightly perforated ; the mammillaiy eminences 

 which support them are small and ring-like with faintly marked 

 crenulations, and the areolas are rather wide and only slightly 

 grooved, so that the tubercles project prominently and abruptly 

 from the surface of the test. The margin of the areolas is en- 

 circled by a row of granules rather larger than those which cover 

 the rest of the intertubercular surface of the plates ; here the 

 granules are close-set and disposed without much regularity. 

 The apical disc is of moderate size and slightly prominent ; the 

 five ovarial plates are large and of a heptagonal form, the ocular 

 plates are small and heart-shaped, and the surface of both is 

 covered with a close-set delicate granulation ; the anal opening 

 is nearly central and circular ; the base is flat ; the mouth- 

 opening is large and widely decagonal from the great span of 

 the ambulacral arches, and the comparative smallness of those 

 of the interambulacra. The spines are as yet unknown. 



Affinities and differences. — This remarkable little Urchin is so 

 entirely different from its congeners, that it is impossible to 

 mistake it for any other of the group to which it belongs. The 

 presence of tubercles at the base of the ambulacral areas only, 

 and of granules on the sides of these spaces, associate it with 

 H. diademata, but the small number of the primary tubercles on 

 the interambulacra, added to the great distance at which they are 

 placed apart, sene to distinguish it from the young of that spe- 

 cies; in fact, these characters alone are perfectly diagnostic of 

 H. minor among all other forms of Hemicidaris. 



Locality and stratigraphical range. — It was first found in the 

 " Grand Oolite " of Langrune, Calvados, from whence the beau- 

 tiful specimen before us was obtained, and kindly sent by Pro- 

 fessor Deslongcharaps of Caen. We take the present opportunity 

 of recording our gi-ateful acknowledgements to that eminent na- 

 turaUst for his kindness and courtesy, not only in contributing 

 specimens to our cabinet for comparison and reference, but 

 likemse for communicating many rare species of oolitic Echi- 

 nidje which served as the types of several of M. Agassiz's spe- 

 cies, and which specimens have been of much service in clear- 

 ing up doubts as to the identity of some other English forms. 

 H. minor was collected in this country by W. Walton, Esq., from 

 the Great Oolite of Hampton near Bath. 



History. — First named by j\I. Agassiz from specimens in 

 M. Michelin's cabinet ; afterwards described as Acrosalenia rari- 

 spina by Prof. M'Coy from sj)ecimens in the Cambridge Museum, 

 which came from Mr. Walton's scries collected near Bath ; it has 



