26 Dr. T. Wright on new Species of Echinodermata 
test, not at all inclined to the pentagonal form of many of its 
oolitic congeners. The ambulacral areas are three-fourths the 
width of the interambulacral areas, and are nearly of a uniform 
width throughout, tapering slightly and gracefully wards to- 
wards their superior third; the contraction assumes the form 
of a gentle curve slightly inclined towards the centre. The 
double row of tubercles gradually increases in size from the 
mouth to the equator, where three pairs are about the same size ; 
from this point upwards they gradually decrease, and terminate 
in two pairs of minute rudimentary tubercles at the disc. A 
single row of granules, arranged in a zigzag form, separates the 
primary tubercles from each other, a larger granule marking each 
of the angles. There is no granulation or other sculpture be- 
tween the mammillary eminences of the tubercles and the pori- 
riferous avenues. There are from twelve to thirteen pairs of 
tubercles in each area. The interambulacral areas are nearly 
;‘sths of an inch in width, and 4th wider than the ambulacral 
areas; they retain their width uniformly throughout, and are 
occupied by two rows of primary tubercles, nine to ten in a row, 
the mammillary eminences of which are large and prominent, 
and separated from each other by two rows of small granules 
which extend only a short distance beyond the equator ; the 
remaining space between their termination and the dise being 
destitute of sculpture, where likewise the areas are slightly de- 
pressed ; and a single row of granules rises on the external side 
of the tubercles, with here and there a secondary tubercle towards 
the basal portion of the test. 
The poriferous avenues are very narrow: the pedal pores are 
arranged in a single file, only three or four additional pairs being 
introduced in the increased spaces around the circumference of 
the mouth. The tubercles of both areas are of moderate size, but 
exceedingly prominent, in consequence of being elevated upon 
large. mammillary eminences, the apices of which are deeply cre- 
nulated. The tubercles of the ambulacral areas at the equator 
are not much less than those of the interambulacral areas, but 
upon the upper surface of the test they become much smaller 
and more numerous, 
The mouth is decagonal and of moderate size: the arches over 
the bases of the ambulacral areas are about one-third greater in 
span than those across the interambulacra. The disc is absent 
in all the specimens, four in number, that we have seen. 
Affinities and differences.—This species resembles Cidarites 
(Diadema) mamillanus, Roemer, in the prominence of the tuber- 
cles and depression of the test ; but Roemer’s figure* is so indi- 
Ms Versteinerungen des Norddeutschen Oolithen Gebirges, pl. 2. 
fig. 1. 
