184 Dr. T. Wright on Fossil Echinoderms 



from the apex of the fasciole, are very characteristic of this spe- 

 cies ; if to these we add the imbricated style of the plates occu- 

 pying the sides of the base, and the oblique way the tubercles 

 are set on their oblong bases, we have an assemblage of organic 

 characters by which B, imbricatus may be readily distinguished 

 from its congeners. The form of the test, the size of the 

 tubercles, the symmetiy of the subanal rosette, formed by radii 

 of tubercles, and encircled by a broad fasciole, readily separate 

 it from B. latus, with which it is associated in the same stratum. 

 Locality and stratigraphical position. — This species was col- 

 lected from bed No. 1, the Gozo marble, at Malta : it is the pro- 

 perty of the Bristol Institution. 



Brissus oblongiLs (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 sulcus ; 

 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 3y*Q inch, transverse 

 diameter l^^^ inch, height ly'^ 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 

 gi'eatest 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 (2 b) is convex, chiefly from the 

 arched form which the sternal portion of the interambulacrum 



