from the Island of Malta. 105 
Description.—This remarkable Urchin wants the symmetrical 
proportions of the other Schizasters met with in the same rocks ; 
it is rounded and broad before, and tapers into a narrow wedge- 
shape process behind ; the dorsal surface inclines forwards at an 
angle of 17°; the ambulacral areas are long. The single anterior 
area compared with S. ewrynotus is narrow, and of a uniform 
width ; it is 1,5, inch in length from the apical disc to the 
fasciole ; there are twenty-four pairs of pores in the avenues, 
the external being much larger than the internal row, although 
this is properly speaking a generic character. The antero-lateral 
ambulacra diverge nearly straight outwards at an angle of 44°; 
they form deep depressions in the test 1,5, inch in length, and 
the zones contain thirty pairs of holes in each: the postero- 
laterals are slightly petaloid, and gently flexed outwards; they 
are 33ths of an inch in length, and diverge at an angle of 60°. 
The zones contain about twenty pairs of holes; the test being 
nearly as broad as it is long across the termination of the an- 
tero-lateral ambulacra; the anterior border is gently rounded, 
and has a rather deep anteal suleus for the ambulacrum ; from 
the same point to the posterior extremity it tapers suddenly, 
which gives a wedge-shaped appearance to the test when viewed 
from above. The most remarkable feature in this Urchin is the 
curious form which the single interambulacrum assumes, owing 
to the great development of this area ; the dorsal surface forms an 
inclined plane having an inclination of 17°; the anterior part is 
therefore very much depressed, and the posterior part much ele- 
vated. The single interambulacrum forms a prominent beak- 
like process, beneath which the posterior border is broad, and 
inclined downwards and forwards; the sternal portion of this 
area 1s prominent and convex, towards which the basal parts of 
the lateral interambulacra slope suddenly forwards and inwards. 
The anus is pyriform, and placed high up underneath the beak- 
like process. The mouth is situated near the anterior border ; it 
has a large under-lip, but is crushed in the small specimen, and 
covered up in all the others before us. The small apical disc lies 
concealed at the posterior third of the dorsum by the prominent 
apices of the lateral interambulacra. The peripetal fasciole takes 
a zigzag course along the outer borders of the ambulacra, and 
from the base of the antero-laterals it passes nearly at right 
angles across the anterior interambulacra to the external side of 
the single ambulacrum, where it makes another angle, then 
passes down the side thereof ;3,ths of an inch, dips into the sul- 
eus and unites with the opposite fasciole. The lateral fasciole 
commences at the angle near the base of the antero-lateral am- 
bulacra, and passes downwards and backwards nearly in a straight 
line over the angle of the posterior border at some distance from 
12 
