608 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
irregular in direction, forming wide, imperfect ridges, nearly obsolete on the anterior part of the trunk, most 
strongly marked on the tail; posterior edges of the scales very minutely crenulated, each with about twelve 
notches. Average length four inches three lines, depth of body about eight lines (specimens occasionally occur 
five and half inches long). 
I have not been able to see, any more than M. Agassiz, the articulating process of the scales in this 
species; but I easily see in several specimens the minute crenulation of the posterior edges, which escaped 
him. The oval imbricating scales, forming a row along the middle of the back, are rather large, the others are 
remarkably small, and form, as M. Agassiz and Sir P. Egerton observe, a strong contrast with those of the 
P. glaphyrus. The lower jaws are sculptured with slightly flexuous oblique ridges; the other bones of the head 
are irregularly granulated and marked with short vermicular ridges. 
Position and Locality—Not very uncommon in the Permian marl-slate of Ferry Hill. 
4th Family. SAUROIDII (4g.) 
Teeth of two kinds in each jaw, a few large, conical, pointed, laniary ones alternating with very nume- 
rous, subequal, minute, teeth en brosse. Scales thick, bony, polished by a layer of ganoine, flat, rhomboidal, 
of moderately large size ; not imbricated, articulated by their edges. Endo-skeleton bony. 
These are slender, swift, carnivorous fishes, with large fins. They are united by Miiller with the Lepidoidii. 
The family is divided into two sections, first, with heterocercal tails, confined to the Palzeozoic rocks ; 
second, those with homocereal tails, extending from the lias to the present seas inclusive. The genera of 
this family extend from the Devonian to the recent periods inclusive, but are most numerous in the Mesozoic 
Rocks. 
Genus. PYGOPTERUS (44g.) 
Gen. Char.—Body large, elongate, ovate ; fins very large, with fulcral scales ; anal fin of moderate depth, 
but very long; dorsal of moderate length, nearly opposite, or a little in front of the anal fin; ventrals small, 
slightly in front of the middle of the body; pectorals moderately small, falcate ; caudal very large, deeply 
notched ; upper jaw a little longer than the lower; endo-skeleton strong; vertebree usually wider than long ; 
scales proportionally rather small, rhomboidal, smooth, and minutely punctured or diagonally striated, extending 
over the pedicles of the fins, and particularly over the thick upper lobe of the tail to the extremity, having 
a moderately wide articular margin, sometimes prolonged at the upper angle, and having a medial, internal, 
articular ridge, which forms a prolongation from the middle of the upper margin. 
PYGOPTERUS MANDIBULARIS (Ag.) 
Ref. and Syn.= Fossil Fish, Sedgwick Trans. Geol. Soc. 2nd Series, Vol. III. t. 10. f. 1, 3 = Nemopteryx 
mandibularis and Sauropsis Scoticus Ag. MSS. names in collections=Pygopterus mandibularis Ag. 
Poissons Fossiles, Vol. II. t. 53. and 58a;?+P. sculptus id. ib. p. 77; = Pygopterus Scoticus, Bronn. 
Lethwa; King Perm. Foss. t. 23. 
Dese.—Body very elongate; head (much shattered, but apparently) trigonal, and as deep as long; pectorals 
large, faleate, two-thirds the length of the space between their base and the origin of the ventrals, which 
space is about equal to the depth of the body at the nape; ventrals of moderate size, triangular, their length 
about two-fifths the depth of the body at their origin; from the origin of ventrals to origin of anal fin slightly 
less than from the same point to the origin of the pectorals, and about equalling the depth of the body at the 
origin of the anal, which is vertically under the middle of the dorsal fin; dorsal and anal fins nearly equal, 
considerably higher than long, the anal narrower and more faleate than the dorsal; pedicle of the tail rapidly 
attenuated from these fins, elongate slender; from origin of anal to middle of base of lower lobe of caudal 
equal to twice the depth of the body between the dorsal and anal fins: caudal very deeply forked, with narrow 
nearly equal lobes; length of the lower lobe equal to one and half the depth of the body between anal and 
