90 Dr. T. Wright on Fossil Echinoderms 
Brissus oblongus (Forbes MSS., n. sp.). Pl. V. fig. 2 a-c- 
Test oblong, depressed before, elevated behind; dorsal surface 
convex ; anterior border rounded, with a slight anteal suleus ; 
antero-lateral ambulacral areas slightly bent forwards, and 
nearly forming right angles with the longitudinal axis; pos- 
tero-lateral ambulacra make an angle of 68°; the anterior are 
shorter than the posterior pair ; posterior border produced and 
truncated : anus large, oval, and placed high up : base convex, 
sternal portion prominent, greatest width across the base of 
the postero-lateral ambulacra. 
Dimensions.—Antero-posterior diameter 2,', inch, transverse 
diameter 1,9, inch, height 1,/; inch. 
Description.—This small Brissus has an oblong form, and is 
rounded before and truncated behind ; the anterior half of the 
test is more depressed than the posterior half ; the single inter- 
ambulacrum rises into a ridge-like eminence on the back, and the 
sternal portion thereof is much inflated at the base, so that the 
greatest height of the test is in this region. The antero-lateral am- 
bulacra (2 a) are shorter than the posterior pair, and are extended 
across the test nearly at right angles to the longitudinal axis ; the 
postero-lateral ambulacra are longer than the anterior, and form 
angles of 68°; the petaloid portions of both areas are depressed ; 
the anterior pair have eighteen pairs of pores, the posterior pair 
have twenty-four pairs of pores in their poriferous zones: the 
single ambulacrum is not lodged in a rudimentary anteal sulcus, 
and is nearly on a level with the contour of the test, the front 
and cheeks of which are convex, with four groups of larger tuber- 
cles in this region ; the sides slope obliquely downwards to the 
border, which is obtuse: the single interambulacrum is raised 
into a ridge above, and produced into a blunted caudal process, ob- 
liquely truncated behind: the base (2d) is convex, chiefly from the 
arched form which the sternal portion of the interambulacrunt 
assumes : the mouth is large, near the anterior third of the base : 
the anus is of an elliptical form, and occupies more than the 
upper half of the truncated portion of the posterior border. The 
peripetal fasciole (2 a) closely embraces the ambulacral pairs, and 
makes three angles in passing over the anterior interambulacra ; 
the subanal fasciole (2 4) describes a heart-shaped outline, its base 
is near the anus, and its apex touches the prominent point of the 
sternum ; the space thereby circumscribed is filled with tubercles 
having a definite arrangement. The apical disc is small, with 
four genital pores, the posterior pair being much larger than the 
anterior pair; the tubercles (2c) on the anterior interambulacra are 
much the largest, those on the rest of the back are small and 
very uniform in size, whilst those on the sternum and the sides 
