from the Island of Malta. 75 
of Westphalia, where it appears to be common. The specimen 
before us is the only one we know from Malta. The circum- 
ference is nearly ovato-orbicular, slightly inclining to an obsolete 
pentagon, with the posterior border most produced. The dorsal 
surface is highly convex, the posterior half being much more so 
than the anterior. The ambulacral areas are unequal, as regards 
length, width and development; the single anterior area is the 
shortest and narrowest, the antero-laterals are next in size, and 
the postero-laterals are the most fully developed; they have all 
a lanceolate form, with blunt apices. The surface of the areas 
is on a level with that of the interambulacra, in the specimen 
before us; but in some of the Westphalian Urchins the ambu- 
lacral areas form convex projections on the surface of the test. 
The poriferous avenues, extending down more than two-thirds of 
the dorsal surface, are well marked in our specimen, and lie in 
depressions of the test ; they consist of two series of pores; the 
internal holes are round, the external run into oblique slits that 
have a direction upwards and inwards; the pores on the right 
and left sides of the areas do not always correspond in length ; 
thus, the anterior pores in the antero-lateral areas are often only 
half as long as those on the posterior side of the same areas, 
and we see a similar inequality, although not to the same 
extent, in those of the single ambulacrum. The anterior and 
posterior pair of the interambulacral areas are much alike in 
form and development; but the single interambulacrum is 
different, it forms a more convex eminence than the others 
above, and is produced into a slight caudal appendage behind. 
The apical disc is small and excentral, situated nearer the an- 
terior border.. The madreporiform body occupies the centre, 
around which the four genital holes are pierced. The base is 
concave ; the mouth is nearer the anterior border, is transversely 
oblong, and surrounded by five lobes, formed by the termination 
of the interambulacra; the posterior single lobe is the largest ; 
the anterior pair are next it in size, and the lobes of the postero- 
lateral areas are the smallest and most contracted. Between 
the five oral lobes, the poriferous terminations of the ambulacral 
areas form petaloidal depressions, which are perforated with 
numerous holes; these run out and form lines which indicate 
the basal boundaries of the areas... The anus is transversely 
oval, ;4,ths of an inch in its long diameter, is more convex on 
its anterior than its posterior border, and is situated close to the 
margin; it is rather larger than the mouth-opening. The 
tubercles are small, uniform in size, and closely set together on 
the dorsal surface, and longer and more widely apart on the base. 
_ Affinities and differences.—The great convexity of the dorsal 
