Pisces. | UPPER PALZOZOIC VERTEBRATA. 613 
I am quite certain, from a comparison of the specimens, that the Holoptychius Portlocki (Ag.) of the fish- 
beds at Cultra, Holywood, near Belfast, and Draperstown, &c., are identical in all characters both of the teeth 
and scales with the H. Hibberti of the Burdichouse and Gilmerton beds. The granulated surface adheres so 
firmly to the matrix, that all the figures of the scales published by Dr. Hibbert and Col. Portlock represent 
only the inner surface. 
The genus Megalichthys of Agassiz and Hibbert was founded originally upon the great teeth of this 
species, which are well illustrated in the 13th volume of the Trans. R. S. of Edinburgh, t. 8, 9, and 10; 
similar teeth are figured under the same name, Megalichthys Hibberti, on Agassiz’ authority, by Dr. Buckland, 
in his Bridgewater Treatise, and Agassiz first allusion to Megalichthys, at page 87 of his second volume of 
the Poiss. Foss., refers to the same plates and figures just mentioned, which leaves no doubt that these gigantic 
teeth and scales were the true original types of Megalichthys. At page 90 of the second part of the same 
volume of his work, however, M. Agassiz describes and figures a totally different, comparatively small, fish, 
with rhombic scales, and teeth about two lines long, as the true Megalichthys; and this latter type unfortunately 
has so monopolised the name that I am advised, against my judgment, to leave it to it. Subsequently Prof. 
Owen, in his Odontography, figured some of the present large teeth as the type of his new genus Lhizodus, 
stating them to be identical with the Holoptychius Hibberti of Agassiz’ MS. list. 
Position and Locality —The large scales and teeth very common in the limestone of the coal-measures 
at Burdiehouse near Edinburgh, also in the fish-beds of Cultra, Holywood, near Belfast, in the similar beds 
at Fermanagh, Draperstown, the large jaws and teeth not uncommon in the similar beds at Gilmerton. 
(Systematic place uncertain.) 
Genus. OSTEOPLAX (J/‘Coy). 
Gen. Char.—Dermal plates large, flat, osseous, polygonal, with straight sides; surface irregularly and 
minutely wrinkled, with scattered pores. Microscopie structwre:—Vertical section shewing large, distant, 
cylindrical, branched, vertical tubes (? Haversian canals) terminating in the pores of the surface; the spaces 
between these tubes containing numerous oval bone-cells, rather more than their own length apart, from each 
of which short radiating branches extend on all sides, about six to the length of a corpuscle. Horizontal 
sections :—large, circular, distant openings of the vertical tubes, with numerous intervening minute, radiated 
Purkinjinian cells, the tubuli of which do not anastomose with those of the adjoining cells in either section. 
One species. 
OsTEOPLAX EROSUS (JM/*Coy). PI. 3. K. fig. 12. 
Ref—M “Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. 
Desc.—Bony plates one to two inches wide and one line thick; edges square; surface with close, short, 
irregularly flexuous, smooth grooves, visible to the naked eye, and with distant irregularly scattered oval pores. 
The remarkable bony plates to which I have given the above name vary in the number of their sides and 
the amount of the angles at which they meet; but the sides are always straight, and the surfaces flat and of 
uniform thickness. It is clear from their form that they cannot belong to the head, but must be viewed as 
dermal bones, covering some part of the body of a mailed fish. Of known genera they can only be compared 
with Psammosteus of the Old Red sandstone, to one species of which, the P. meandrinus (Ag.), the resemblance 
is particularly close; but 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 
composed of horizontal layers of large irregular cells, while Osfeoplaw has well developed, radiated hone- 
corpuscles. 
Position and Locality.—Not uncommon in the schists belonging to the base of the carboniferous series 
at Cultra, Holywood, county Down, Ireland. 
Explanation of Fiqures.—P\, 3. K. fig. 12, portion of one of the plates natural size, from the lower 
earboniferous shales of Cultra, Holywood, county Down; fig. 12a, ditto portion of surface magnified. 
