from the Island of Malta. 183 



two only are figured, and for this reason we are unable to make 

 a comparison with them. 



Locality and strntigraphical 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- 

 rior border; sternal portion of the intcrambulacrum with a 

 regular ornamentation. The subanal fasciole 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 iuterambulacral 

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

 rying an oval eminence vnth 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 injm'ed. 



Dimensions. — Autero-posterior diameter Sy^^ inches, transverse 

 diameter 3 inches, height j^jjths of an inch. 



Description. — The detailed diagnosis given of this species con- 

 tains nearly all that we can describe of this Brissus, foi-, 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 band of microscopic 

 granules, and the leaf-like tuberculated expansion which extends 



