from the Lias and Oolites. 23 



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

 five ovarial plates are laru'- 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, serve 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 Laugrune, Calvados, from whence the beau- 

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

 fessor Deslongchamps of Caen. We take the present opportunity 

 of recording our grateful acknowledgements to that eminent na- 

 turalist for his kindness and courtesy, not only in contributing 

 specimens to our cabinet for comparison and reference, but 

 likewise for communicating many rare species of oolitic Echi- 

 nidse 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 M. Agassiz from specimens in 

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

 spina by Prof. M'Coy from specimens in the Cambridge Museum, 

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

 never yet been found either by Mr. Lycett or ourselves in the 

 Great Oolite of Minchinhampton. 



Acrosalenia crinifera, Wright. PL II. fig. 1, a-d. 



SYN. Echinus minutus, Buckman, Geology of Cheltenham, 2nd ed. 



p. 95. 

 Cidarites criniferus, Quenstedt, Handbuch der Petrefactenkunde, 



tab. 49. fig. 32. p. 574. 



Test circular, depressed; ambulacral areas narrow, \\ith t \\orows 

 of microscopic tubercles placed at some distance apart on cadi 



