from the Island of Malta. 89 



rior border ; sternal portion of the interambulacruin with a 

 regular ornamentation. The subanal fascicle very near the 

 anus is heart-shaped and narrow ; it encloses rows of tubercles 

 which are arranged in radii in regular order; before the 

 fasciole the test forms a projection, and from the summit 

 thereof, rows of tubercles arranged in straight lines extend 

 towards the mouth, increasing in size as they approach that 

 opening ; the basal portions of the other interambulacral 

 areas are covered with scale-like imbricated plates, each car- 

 rying an oval eminence with a crenulated summit, and a 

 tubercle placed at the anterior side of the oval eminence; 

 these tubercles are all regularly arranged in rows which have 

 a direction forwards and outwards : the postero-lateral ambu- 

 lacra form a naked space, which separates the imbricated basal 

 portions of the pairs of interambulacra from the ornamented 

 sternal portion of the single one. The anus is large and 

 situated at the posterior border ; both this opening and the 

 mouth are much injured. 



Dimensions. Antero-posterior diameter 3-j^ inches, transverse 

 diameter 3 inches, height r 8 n ths of an inch, 



Description. The detailed diagnosis given of this species con- 

 tains nearly all that we can describe of this Rrissus, for, with the 

 exception of a small portion of its anterior part preserving a por- 

 tion of the peripetal fasciole, all the rest is absent ; the regu- 

 larity in the arrangement of the tubercles at the base constitutes 

 a characteristic feature of this form, and the imbricated style of 

 the basal plates, resembling the tegumentary membrane of a 

 placoid fish, gives value to the specific name. 



Affinities and differences. The order and symmetry of the de- 

 coration of the sternal portion of the interambulacrum, the 

 heart-shaped subanal fasciole, with its broad baud of microscopic 

 granules, and the leaf-like tuberculated expansion which extends 

 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 \vay 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 symmetry 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 stratiijnijiltical position. This species was col- 

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

 perty of the Bristol Institution. 



H2 



