from the Island of Malta. 113 
convex ; tubercles moderate in size ; mouth transversely ob- 
long, situated at the junction of the anterior with the middle 
third ; tubercles on the upper surface very small. 
Dimensions.——A German type specimen. Antero-posterior dia- 
nig 2445 inches, transverse diameter 2,5, inches, height 1,5 
inch. 
A Maltese specimen. Antero-posterior diameter 1,8, inch, 
transverse diameter 1-/, inch, height }Zths of an inch. 
Description.—This Urchin is well known from the admirable 
figure in Goldfuss. Its upper surface is more convex and in- 
flated than in the other congeneric species; it is higher behind 
than before, and has a blunt ridge which passes backwards from 
the disc to the border. The antero-lateral petaloidal ambulacra, 
28ths of an inch in length, curve a little outwards, forming an 
angle of 18°; their zones contain from twenty-two to twenty- 
four pairs of pores, separated by rather thick partitions of the 
test. The postero-latera]l areas are narrower than the anterior 
pair, and rather more than an inch in length; their zones con- 
tain from twenty-eight to thirty pairs of holes, and they form 
angles of 60°. The interambulacral areas are wide and largely 
developed in this species ; the upper plates in these areas, lying 
between the ambulacra, support only very small perforated 
tubercles, arranged in groups of threes and fours, and disposed 
on all the areas; this character serves to distinguish S. Des- 
marestii from all its congeners at present known: the small 
tubercles on the dorsal surface are very small, and closely set 
together. The single ambulacrum is lodged in a broad shallow 
valley, which forms however a considerable anteal sulcus; the 
pores in this area are so much covered up with matrix in our 
specimen, that we are unable to count their number. The pos- 
terior border is truncated, and the large transversely oval anal 
opening occupies the upper part of this region. The shelly 
matrix entirely conceals the course of the subanal fasciole. The 
sternal portion of the interambulacrum is slightly convex, and 
covered with small tubercles that radiate in lines in all direc- 
tions from a central point ; the basal portions of the anterior and 
lateral interambulacra are covered with larger tubercles, and the 
naked intermediate spaces indicate the ¢rajet of the basal por- 
tions of the postero-lateral ambulacra from the border to the 
mouth, The mouth is situated at the junction of the anterior 
with the middle third; it is much elongated transversely, and 
has five poriferous petals surrounding it. The apical dise is 
small and nearly central ; it has four genital holes and five small 
eye-holes. 
Affinities and differences.—The inflation of the test, the small- 
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