Pisces. | DEVONIAN VERTEBRATA. 589 
Genus. TRIPLOPTERUS (M Coy). 
= Tripterus M°Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. 
Gen. Char.—General shape of the body and form of the plates of the head and body as in Osteolepis, but 
having only one dorsal fin, which is precisely over the first anal fin. 
The fishes of this genus are very much allied to Osfeolepis in general habit, but instead of having two 
dorsal alternating with two anal fins, there is but one dorsal, which instead of alternating with or being 
vertically over the interval between the anal fins (as would be the case in Ostcolepis, if only one fin were 
preserved), is precisely over the first anal, as in Diplopterax, (= Diplopterus Ag.), which it also greatly resembles, 
but from which it differs in wanting the second dorsal, and in haying a perfectly heterocercal tail—a character 
which I have ascertained does not exist in Diplopterax. The name Tripterus having been preoccupied, I have 
changed it as above. 
TRIPLOPTERUS POLLEXFENI (M/°Coy). Pl. 2. D. fig. 5. 
Ref.= Tripterus Pollexfeni M°Coy, Ann. Nat. Hist. 2nd Series, Vol. II. 
Desc.—Ovate, gradually tapering from the head, which is broad, depressed, semi-elliptical, obtusely 
pointed in front, its width at base equal to its length, and being about one-fifth the entire length of the fish ; 
pectoral fins small, broad, ovate, their height about two-thirds the width of the body at their base; tail small, 
perfectly heterocercal, retral margin very concaye, and the upper lobe twice the length of the lower; two anal 
fins nearly equal, triangular, one-third higher than long, rather more than their own height apart, the second 
almost touching the caudal fin; dorsal fin narrow, ovate, almost twice as high as long, precisely over the first 
anal; scales rhomboidal, those of the body flat, about one-third higher than long, those of the tail longitu- 
dinally gibbous, lozenge-shaped, and about twice as long as high; under the lens they are all very minutely 
and uniformly punctured, as in Osteolepis and Diplopterus. Total length about seven inches, greatest width of 
body one and quarter of an inch, length of body-scales one and half line. 
So completely identical are the plates of the head of this fish with those of the large imperfect example 
figured by Agassiz, (Poiss. Foss. Vol. 11. Plate 2 4, fig. 2), that I cannot help suspecting that that figure may 
represent a portion of a fish of the present species, the imperfection of the retral part of the body having 
perhaps permitted M. Agassiz to refer it to the Osteolepis macrolepidotus ; although even without seeing the 
fins we might distinguish it by its wide, rapidly tapering figure from that species, which is correctly represented 
by the figure 1 of the same plate, so far as it goes. The teeth are minute, slender, conical, rather distant, 
apparently in several rows, and of irregularly unequal size. I have examined three perfect specimens of this 
species presented to the University collection by the Rev. W. Pollexfen, by whom nearly all the Orkney 
fishes here noticed were collected, and whose zeal I am happy to commemorate by dedicating this to him. 
Position and Locality —Not uncommon in the Old Red sandstone at Orkney. 
Explanation of Figures—PI. 2. D. fig. 5, small specimen, natural size ; fig. 5 a, scale of ditto magnified 
three diameters, shewing the polished, punctured surface, and broad articular margin; 5 0, scales of ditto, 
natural size, from another specimen. 
5th Family. CCZLACANTHI. 
Scales polished, variously ornamented, rounded, largely imbricated; teeth conical, longitudinally plaited 
at the base, of two sizes, the smaller very numerous, the larger few, far apart, and set rather within the line of 
the smaller ones. 
The scales composed of a bony plate covered with ganoine ; bones of the head also polished and generally 
granulated. A transverse slice of a tooth magnified shews the medullary cavity sending off innumerable 
radiating, vertical, branching fissures, about which the dentine is folded. 
