from the Island of Malta. 95 
cated: anal opening high near the upper surface : apical disc 
small and central. 
Dimensions.—Antero-posterior diameter 258, inches, transverse 
diameter 3 inches, height 1,8, inch. 
Description.— The orbicular form and inflated sides of this 
Urchin, with its large, deep, diverging ambulacra, and greater dia- 
meter in the transverse than in the longitudinal direction, impart 
to it an air which widely distinguishes it from other Hemiasters. 
The single ambulacrum is narrow and shallow, and forms an in- 
considerable anteal sulcus, which measures 1, inch in length 
from the apex to the fasciole; it has a single row of lateral 
holes and accompanying tubercles of small size placed near each 
other within, and the holes only at considerable distances apart 
without the fasciole. The antero-lateral ambulacra are rather 
wider and much deeper than the single area ; they are 1,3, inch 
in length, and are directed forwards and outwards, forming 
an angle of 25°; the walls of the depression are formed by 
the poriferous zones, and the base by the intervening smooth 
space between them: the postero-lateral ambulacra are directed 
obliquely backwards and gently curved inwards ; they are 1 inch 
long and form an angle of 62°: the peripetal fasciole closely 
embraces the base of the areas, and maintains a nearly uniform 
width throughout its course: the test is very much inflated an- 
teriorly and laterally, and its posterior border is abruptly trun- 
cated: the single interambulacrum is elevated into a ridge, 
which rises between the two posterior ambulacra, at the termi- 
nation of which the anal opening is situated : the test is covered 
with small, nearly equal-sized tubercles, which are larger on the 
fore-part, cheeks, and sides than elsewhere: the apical dise is 
small, and lies in a depression at the centre of the test, the 
apices of the interambulacra rising into little eminences around 
it: the base is entirely concealed by the matrix. : 
Affinities and differences.—This large species differs so much 
from its congeners in its breadth, in the depth and divergence of 
the antero-lateral ambulacra, which are likewise slightly curved 
forwards, in the length and depth of the posterior pair, which 
equal the single ambulacrum in length, in the breadth and extent 
of the peripetal fasciole, and the perpendicular truncature of the 
posterior border, with the general tumidity of its sides, that it is 
readily distinguished from them. 
Locality and stratigraphical position.—It was collected from 
bed No. 4, the calcareous sandstone at Malta, and is one of the 
few tertiary Urchins in our cabinet; it is the only specimen of 
the species we have seen. 
