hy from the Lias and Oolites. 23 
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, 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 Langrune, 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 emment 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- 
nidz 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 rari- 
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. PI. II. fig. 1, a—d. 
Syn. Echinus minutus, Buckman, Geology of Cheltenham, 2nd ed. 
. 95. 
Cidarites criniferus, Quenstedt, Handbuch der Petrefactenkunde, 
tab. 49. fig: 32. p. 574. 
Test circular, depressed ; ambulacral areas narrow, with two rows 
of microscopic tubercles placed at some distance apart on each 
