96 Dr. T. Wright on Fossil Echinoderms 
Hemiaster Cotteauit, Wright. Pl. VII. fig. 2 a-d. 
Test orbicular, globose, much inflated, declining anteriorly, ele- 
vated posteriorly, the interambulacrum forming a prominent 
carina which terminates in a tail-like process above the anus ; 
posterior border obliquely truncated ; ambulacral areas deeply 
sunk; an anteal ambulacrum forms the sulcus in the anterior 
border; antero-laterals long, and inclined to 45°; postero- 
laterals one-half the length of the anterior pair, inclined to 
57°; apical disc nearly central; peripetal fasciole broad and 
undulating ; anus high under the carinal process; tubercles 
larger on the sides and base than on the dorsal surface ; 
mouth labiate near the anterior border. 
Dimensions.—Antero-posterior diameter 1} inch, transverse 
diameter 132 inch, height 134 inch. 
Description —This Urchin has a globose form, and is much 
inflated at the sides; the dorsal surface is convex, and declines 
much more rapidly from the apical disc to the anterior border, 
than from the disc to the posterior border. The ambulacral 
areas (2a) are all deeply sunk; the single ambulacrum is the 
longest, and forms a considerable anteal sulcus; the antero-lateral 
pair have a gentle double curve; they are ;%ths of an inch in 
length, and form an angle of 45°. The number of pores (2c) 
in the avenues is twenty-two pairs in the inner, and twenty-four 
in the outer zone; the postero-lateral pair are scarcely half the 
length of the anterior pair; they incline at 57°; their number of 
pores is ten and twelve pairs. The peripetal fasciole (2 d) closely 
embraces the ambulacral star; a naked track proceeds from the 
base of the antero-laterals to the mouth, indicating the course 
of the imperforate portion of the ambulacral areas: the rapid 
declivity of the anterior part of the test strongly contrasts with 
the inflated condition of the sides and the elevation of the in- 
terambulacrum ; from the centre of this area a ridge rises which 
is produced into a tail-like process, and beneath, the posterior 
border is scooped out, and truncated obliquely downwards and 
inwards. The anus is situated high up, immediately beneath 
the caudal prolongation ; the base is convex, and a partially 
naked space on each side of the sternal portion of the inter- 
ambulacrum, indicates the track of the basal portions of the 
posterior ambulacra. The tubercles of the upper surface (2 6) 
are smaller and more closely set together than those on the 
sides and base, where they are larger, wider apart, and more 
fully developed. They are perforated and uncrenulated, and 
surrounded by a circle of small tubercles. H. Cotteauii resembles 
Spatangus (Hemiaster) acuminatus, Goldf., but it is more globose, 
and its posterior half is neither so elevated, nor yet so wedge- 
