Pisces. ] DEVONIAN VERTEBRATA. 585 
DIPLACANTHUS PERARMATUS (M/‘Coy). PI. 2. B. fig. 3. 
Ref —M Coy, Ann. Nat. Hist. 2nd Series, Vol. IT. 
Desc.—Body thick, short, fusiform ; tail very short, nearly square, its width only two-thirds the length of 
the second dorsal spine, the upper lobe projecting but little beyond the lower ; spines smooth, extremely long, 
first dorsal equal in length to the space between the first and second dorifils, slightly less than the depth of 
the body at its base, gently curved; posterior spine straighter, and about one-eighth longer than the anterior ; 
pectoral spines half the length of the second dorsal; anal spine curved, only two-thirds the length of the 
second dorsal; ventral, medial, and thoracic spines slightly curved and of moderate length; scales slightly 
higher than wide, nearly flat, minutely granulated (the impressions only seen), about three in the space of 
one line. Length, from the base of the pectoral fin to the tip of the tail four and half inches. 
This is most allied to the D. longispinus (Ag.), but has still longer spines, the second dorsal being 
especially remarkable ; the dorsal spines are much longer in proportion to the distance between them and the 
depth of the body ; the anal spine being, on the other hand, comparatively shorter ; the tail is still smaller, and 
more equal-lobed, and the scales much smaller, and, with the proportion of length to width, reversed: I 
am doubtful about their surface, but the impressions seem distinctly, though minutely and irregularly 
granulated. 
Position and Locality —Rare in the Old Red sandstone flags of Orkney. 
Explanation of Figures.—P). 2. B. fig. 3, natural size of specimen wanting the head; fig. 3a, scales of do. 
from near the middle, magnified 24 diameters. 
DIPLACANTHUS STRIATUS (Ag.) 
Ref.—Ag. Old Red, t. 14. fig. 1 to 5. 
Desc.—Length about two and half inches; greatest depth about seven or eight lines; first ray of each 
dorsal slightly longer than the depth of the body at their base, the first dorsal ray, which is the largest, about 
one line in diameter; the bony ray of each fin finely sulcated longitudinally, about ten sulci on each side, 
slightly curved backwards ; lobes of the tail pointed, the upper lobe twice the length of the lower; scales very 
small, smooth, obtusely rhomboidal, having a large vertically diagonal oval protuberance nearly in the middle 
of each. 
Position and Locality.—Old Red sandstone flags of Orkney. 
3rd Family. SAURODIPTERIDA (4y.) 
Dese.—Body fusiform, robust ; scales large, strong, polished by a thick layer of ganoine, rhomboidal, not 
imbricating, but either with their edges in juxtaposition, or articulated with each other, by distinct bony 
processes, with in general a finely punctured surface (through which the minute nutrient vessels passed to the 
external integument) ; head wide, flattened; teeth numerous, conical, equal (? with simple pulpy cavity), and 
set in the intermaxillaries (as in ordinary fishes), thus differing from the Acanthodide; pectoral fins moderate, 
ventrals small, at about the middle of the body; behind which are two large anals, having two similar dorsals 
opposite, or alternating with them; none of the fins have bony spines; tail heterocercal or diphycercal* ; 
skeleton partially ossified. 
Genera: \st, Diplopterax ; 2nd, Osteolepis; 38rd, Triplopterus, &e. 
* T have proposed this name (from d:puys, duas habens naturas, and képxos, cauda) in the Annals of Nat. Hist. for 
November 1848, to designate the peculiar structure and form of the tail in Diplopteraz, and Gyroptychius, which is inter- 
mediate in some respects between the homocercal and heterocercal types of tail described by Agassiz. In the “homocercal” 
or ordinary form of tail of most recent, and the newer fossil fishes, we usually find a few of the last vertebrae anchylosed, 
and from the terminal mass so formed, the greater portion of the caudal fin is developed, as much from the upper as from 
the lower aspect, and only the few short rays at the commencement of the fin being intercalated with the spinous processes 
4p 2 
