88 Dr. T. Wright on Fossil Echinodcrms 



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 (1 c), and surrounded by 

 a smooth depressed areola; the base is slightly convex; the sternal 

 portion of the single interarnbulacrum 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 fascicle 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 lip ; 

 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 dis'c (1 b) is placed near 

 the centre of the back, about y%ths of an inch before that point : 

 the madreporiforrn 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 

 in the ambulacral areas, and the depth of the anteal sulcus, form 

 a group of characters by which Brissus latus 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 EarlDucie'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 cither 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- 



