from the Island of Malta. 85 
slightly flattened at the cheeks, bulging out at the sides, and 
from thence tapering abruptly towards the posterior border, 
where it is truncated obliquely downwards and forwards; the 
anterior part of the test is flattened and depressed, and the pos- 
terior portion much elevated, from the circumstance of the single 
interambulacrum forming two prominent ridges, one on the 
dorsal, and the other on the basal surface, which gives increased 
depth to the test, tilts it up, and forms an inclined plane of the 
dorsal surface. The petaloidal ambulacra are short, broad and 
leaf-like ; the anterior pair are slightly flexed forwards and form 
an angle of about 15°; their anterior poriferous zone is nearly 
as complete as the posterior zone, which contain respectively 
sixteen and eighteen pairs of pores ; the posterior pair form two 
oval leaflets, the bases and apices of which are nearly equally 
curved, and closed with pores, having about eighteen pairs of 
pores in each zone ; they describe an angle of about 60°. The 
single anterior ambulacrum makes a very slight depression on 
the upper part of the anterior region, and the anteal sulcus 
formed by it is inconsiderable when compared with other con- 
generic forms ; the anterior and lateral pairs of interambulacra 
carry a few large crenulated and perforated tubercles on the 
upper part of their dorsal surface ; on the anterior pair there are 
from seven to eight, and on the posterior pair from four to five 
of these tubercles, which are neither so large nor yet have such 
deep areolas as their homologues in S. Hoffmann. The single 
posterior interambulacrum is narrow, but greatly developed in 
the vertical diameter ; above, a blunt prominent ridge commences 
near the apical disc and extends to the posterior border ; below, 
another ridge commences a short distance from the truncated 
portion of the border, and extends to the centre of the mouth ; 
the base is slightly convex from side to side, besides being 
raised in the middle of its posterior part by the ridge just 
alluded to. The tubercles on the basal portions of the anterior 
and posterior interambulacra are not very large, but are disposed 
with great regularity ; those on the ridge-like prominence of the 
single interambulacrum are arranged in lines which radiate in 
all directions from a point ; those on the pairs gradually decrease 
in size from the mouth to the border; between these two groups 
of tubercles there is on each side a smooth track, corresponding 
with the course of the postero-lateral ambulacra from the border 
to the mouth : the anus is large and circular, and occupies the 
upper part of the posterior border ; the subanal fasciole is de- 
nuded; the mouth is likewise large and transversely oval, and is 
situated near the anteal sulcus. The apical disc is excentral, 
being situated about the anterior part of the middle third of the 
test ; it is small, and is perforated with four genital holes. The 
