614 BRITISH PALAXOZOIC FOSSILS. [ Pisces. 
6th Fam. PYCNODONTI. 
Teeth, obtuse rounded, or obtusely polygonal, depressed, root hollowed and adhering to the jaw (thus 
differing from those of Cestracion), placed in several rows. 
Scales, large, flat, rhomboidal ; articulated by a medial projecting ridge on the under surface, 
Skeleton, bony. 
Body, compressed, flattened, sub-rhomboidal, or broad ovate. 
The appearance produced by the continuous, internal, articulating ridges of the scales, forming oblique 
ridges across the interior of the fish, deceived M. Agassiz, who describes them as parts of the endo-skeleton 
under the name of sternal and nuchal pieces; Sir P. Egerton was the first to rectify this point. 
Short, compressed fishes, with small fins, and teeth fitted for crushing crustacea and shells, 
Genus. PLATYSOMUS (Ag.) 
? = Globulodus (Miinst.) 
Gen. Char.—Rhomboidal, much compressed ; dorsal and anal fins nearly equal and opposite each other, 
the former extending from the middle of the back nearly to the tail; pectorals small; ventrals small, nearly 
under the pectorals; teeth clavate, crown dilated, flattened, base slender, a strong constriction marking the 
lower boundary of the ganoine. Scales large, oblong, having a strong bony articular internal ridge along the 
anterior edge, terminating in a bevelled spine at the upper corner, received into a notch in the lower end of 
the adjoining scale (these articular ridges most strongly marked along the dorsal margin). 
Sir P. Egerton has recommended the classing this genus with the Pycnodontoid fishes, rather than with 
the Lepidoidei, from the mode of articulation of the scales, and from the teeth. 
The genus is found in the carboniferous and magnesian limestones. 
PLATYSOMUS STRIATUS (Ag.) 
Ref. and Syn—Ag. Poissons Fossiles, Vol. II. t. 17. f. 1, 2,3; King and Egerton, Perm. Foss, t. 27, and 
t. 28. f. 1 = Uropteryx striatus Ag. olim + Platysomus parvus, Ag. Poissons Fossiles, Vol. II. t. 18. f. 3. 
Desc.—Greatest width (or depth) of body, which is at the origin of the anal fin, slightly less than from 
the same point to the end of the mouth; dorsal fin commencing a little behind the line of the anal, the profile 
from the origin of the dorsal to the occipital crest nearly straight, moderately sloped with very slight convexity, 
obtusely deflected at the occipital crest at an angle of 145°, continuing thence almost directly to the tip of the 
snout with little more convexity than the dorsal line; line of back straight and abruptly sloped at an angle 
of 120°; from the origin of the dorsal to the pedicle of tail at end of dorsal, a line equal in length to that from 
the origin of dorsal to occipital crest; length and width of the broad portion of the base of tail about equalling 
one-seventh of the greatest depth of the body, the upper angle prolonged into an abruptly attenuated support 
to the upper lobe of the caudal fin, which is deeply forked; the lower lobe rather longer than the upper, the 
length of the upper being about three and half times the width of the pedicle; ventral margin less angulated 
than the dorsal, more conyex in its anterior and posterior portions, and more broadly rounded in the middle ; 
anal and dorsal fins nearly equal, in each the tenth or twelfth ray being the longest, the preceding ones rapidly 
diminishing in size to the first, and the twelve or fourteen succeeding ones rather rapidly diminishing in 
size, after which they taper very slightly towards the posterior end, presenting a nearly straight edge with 
a higher anterior portion; ventrals placed between the anterior and middle third of the space between 
the head and origin of anal fin; form of pectoral and yentral fins unknown; scales closely marked with 
fine, obtuse, subequal, irregularly interrupted undulating striz, either nearly parallel with the longer margitis, 
as in the deep scales of the flanks, or diagonal in position, running from the upper and posterior edges towards 
the anterior and inferior, as on the more nearly equilateral scales (about twelve strie in the space of one line). 
Average greatest depth of body from five to six inches; proportions, taking the greatest depth of the body at 
origin of anal fin as 190; length from posterior edge of head to posterior end of anal fin or pedicle of tail ;%, 
5. 
length of head =, depth of head #, length of lower lobe of caudal fin =, depth of dorsal and anal fins jj; at 
