98 Dr. T. Wright on Fossil Echinoderms 
chloritée near Havre,” and as no species of Urchin known to us 
passed from the secondary to the tertiary epoch, we must reject 
the high authority of this most accurate naturalist, and consider 
the Urchin before us as distinct from S. crassissimus. The test 
inclines to an oblong form (1 ¢) ; it is higher behind than before, 
and declines more rapidly from the disc to the anterior border than 
from the disc to the anus. The ambulacral areas lie in deep 
depressions; the single ambulacrum (1e) is the longest, and forms 
an inconsiderable anteal sulcus ; the antero-laterals are ;‘,ths of an 
inch in length, and form an angle of 44°; the number of the 
pores (1 f) in the zones is fifteen and twenty: the postero-laterals 
are scarcely one-half the length of the antero-laterals ; they form 
an angle of 56°; the number of pores in them is respectively seven 
and ten : the peripetal fasciole is broad, but feebly marked, and 
closely embraces the bases of the areas: four sulci (1 a), nearly 
destitute of tubercles, mark the course of the ambulacra from 
the side of the fasciole to the mouth: the lateral interambulacra 
are rather inflated, and marked by five or six angular elevations 
(1 c) of the test: the single interambulacrum is elevated on the 
dorsum (1a), squarely truncated on the posterior border, and 
convex beneath: the small oval anus is situated very high up, 
about ;$,ths of an inch from the dise: the sternal portion of the 
interambulacrum (1 4) is convex and prominent, and is covered 
with close-set tubercles, arranged in lines, proceeding like radii 
from a central point of the base: the mouth has a large pro- 
jecting under-lip. The upper part of the shell is covered with 
small close-set uncrenulate tubercles (1d), which are larger 
and irregularly disposed on the front and base: the apical disc 
is small and nearly central: there are only two genital heles 
at the apices of the lateral ambulacra: the five eye-holes are 
very small. Whether one pair of genital holes may be a generic 
character of Hemiaster, we have not the means at present of de- 
termining, as most of our specimens of this group have the disc 
concealed ; but about the beautiful H. Sci//le now before us there 
can be no question. 
Affinities and differences.—The absence of the dorsal carina 
and caudal process serve to distinguish H. Scilla from H. Cot- 
teauit ; the latter is likewise a more globose and less elegant form 
of Urchin, and has the truncature of the posterior border down- 
wards and forwards, whereas in H. Scille the direction is down- 
wards and backwards. 
Locality and stratigraphical position.—Collected from No. 4, 
the calcareous sandstone at Malta, from whence the original spe- 
cimen figured by Scilla was obtained: this reason will suffice for 
the name we have given it. 
