88 Dr. T. Wright on Fossil Echinoderms 
tero-laterals themselves ; the rest of the dorsal surface is covered 
with small tubercles closely set together ; each tubercle is perfo- 
rated and raised on a crenulated eminence (1c), and surrounded by 
a smooth depressed areola; the base is slightly convex; the sternal 
portion of the single interambulacrum is rather prominent be- 
hind, but slopes gently towards the mouth; it has an elevated 
ridge in the centre, and is covered with tubercles of a larger size 
than those of the upper surface, and which are arranged in re- 
gular rows. The subanal fasciole is of considerable extent, it 
forms a semicircle which passes across the most prominent part 
of the base, and sends its cornua upwards at a considerable 
distance from the anus ; the basal portions of the pairs of the 
interambulacral areas are covered with tubercles similar to those 
on the sternal part ; a naked track corresponding to the postero- 
lateral areas separates these tuberculated portions of the base. 
The mouth is situated near the anterior border, it is widest in 
the transverse diameter, and has a thick projecting under hip ; 
the terminations of the ambulacral areas surround the mouth, 
and form poriferous zones around that opening: the anus is 
situated beneath the margin in an oblique truncation of the 
posterior border ; the opening is much crushed in our specimen, so 
that its form is not discernible. The apical disc (1 4) is placed near 
the centre of the back, about ;4,ths of an inch before that point : 
the madreporiform tubercle is small and pyriform, and is situated 
behind the four genital pores: the margin of the shell is thin 
and acute. 
Affinities and differences.—The breadth of the test and the de- 
pression of the dorsal surface thereof, with the curve forwards 
i the ambulacral areas, and the depth of the anteal sulcus, form 
a group of characters by which Brissus /atus is readily distin- 
guished from its congeners. Out of the seven fossil species, 
registered but not described in Agassiz and Desor’s Catalogue, 
two only are figured, and for this reason we are unable to make 
a comparison with them. 
Locality and stratigraphical range—Only one specimen of this 
species, in the Earl Ducie’s cabinet, was collected from bed No. 1, 
the Gozo marble, at Malta, so that we conclude the species is 
rare, as it is not contained in either of the other collections of 
Maltese Urchins examined by us. The Jermyn Street Museum 
contains a specimen, which is supposed to be identical with this 
form. 
Brissus imbricatus (Wright, n. sp.). 
Test oblong, much depressed ; no anteal sulcus ; peripetal fasciole 
narrow, lodged in a groove; rest of the dorsal surface frac- 
tured ; base convex ; mouth large, and situated near the ante- 
