FISH OF THE CARBONIFEROUS PfiRIOD. 7 



the ridges of the surface are smooth in the present species and 

 crenulated in the former. The two genera are well-distinguished 

 by the internal microscopic structure, Psammosteus being com- 

 posed of horizontal layers of large irregular cells, while Osteo- 

 plax has well-developed radiated bone-corpuscles. 



Not uncommon in the schists belonging to the base of the 

 carboniferous series at Cultra, Hollywood, county Down, Ireland. 



{Col. Cambridge University.) 



Psammosteus granulatus (M'Coy). 



Sp. Char. A thin, shagreen-like expansion closely covered with 

 nearly uniform hemispherical smooth tubercles, less than half 

 their diameter apart (two in the space of a line), the base of 

 each surrounded by a circle of minute granules. 



This is an irregular fragment of rough shagreen-like integu- 

 ment, measuring about 2\ inches in length and \\ inch in 

 width j it is exceedingly thin. The species is closely allied to the 

 Psammosteus arenatus (Ag.) of the Riga old red sandstone, but 

 is distinguished by the tubercles having no sort of linear arrange- 

 ment, and the granules surrounding the base are proportionably 

 larger and rounder, not seeming like stellular denticles as in 

 that species. 



The specimen is from the fine black shale of the yellow sand- 

 stone (or lowest portion of the carboniferous system) of Kesh, 

 river Banagh, county Fermanagh, Ireland. 



(Co/. Mr. Griffith.) 



Psammosteus vermicularis (M^Coy). 



Sp. Char. Surface covered with very minute conical tubercles, 

 about six in the space of a line, irregularly placed, but avera- 

 ging their own diameter apart, isolated, or two, three or four 

 confluent to form small, irregularly twisted, vermicular ridges ; 

 the sides of the ridges and base of the tubercles denticulated 

 with angular radiations (as in P. arenatus). 



The specimen described is a reniform, convex plate, rather more 

 than half a line thick, 1 inch 9 lines long and 1 inch wide, most 

 probably belonging to the side of the head ; not exactly agreeing 

 with any bone I know in shape, but most like an operculum. The 

 under surface is smooth (except the nucleus), the outer surface 

 closely sculptured as above-mentioned. This species has the cre- 

 nulations of the P. arenatus (Ag.), but the irregular, minute, 

 and frequently confluent granules of the P. undulatus (Ag.) ; it is 

 most nearly allied to the latter species, but the asperities, besides 

 being crenulated, are smaller, more irregular, and the confluent 

 ones more twisted and vermicular. The minute microscopic 



