592 BRITISH PALAZOZOIC FOSSILS. [ Pisces. 
Osteolepis were quadrate, and simply in contact by their edges, and we must class it with Holoptychius, Glyp- 
tolepis, &e. in the family of Cwlacanths, according to the last definition of that group in M. Agassiz’ Mono- 
graph on the Fiskes of the Old Red Sandstone; in fact the relation to this latter genus becomes in this 
light so close that I do not at present see how to distinguish them; and although the great depressed G. 
leptopterus (Ag.), with its strong, bony, lenticular scales, seems distinct from the small Dipteri, yet the 
smaller, lateral compressed specimens of the same species come much closer in appearance; and in either 
case the characters of the number and position of the fins, form and surface of the scales, and the external 
characters of the teeth, are identical in both, pointing to a union of the genera Glyptolepis and Dipterus. The 
latter being much the oldest, would, in this case, of course, be retained. 
The perfectly heterocercal tail and circular imbricated scales now widely separate these fishes from 
Diplopteraz (= Diplopterus Ag.). According to Mr Miller (Witness newspaper, Dec. 23, 1848) the genus 
Polyphractus (Ag.) is formed on the occipital plates of this genus, and he also there states that the teeth 
are exclusively palatal, “blunt, squat, and arranged in two rectangular patches,” identical with those forming 
the genus Ctenodus (Ag.), which he unites thus to the present genus. 
DIPTERUS BRACHYPYGOPTERUS (Sedg. and Murch.) 
Ref—Sedg. and Murch. Geol. Trans. 2nd Series, Vol. III. Pl. 17. 
Desc.—Gradually tapering from the base of the head; length about seven inches, depth nearly one and 
half inches; head small, only one-fifth of the length; posterior anal wider and shorter than in the D. macropy- 
gopterus, not extending more than half way to the angle of the lower lobe of the caudal ; lateral line much 
nearer the dorsal than the ventral margin; scales of the flanks two lines in diameter, varying towards the 
abdomen to nearly three lines ; height (diameter) of the exposed portion of each scale when in situ about twice 
the length thereof; surface strongly marked with concentric imbricating wrinkles on the exposed part, and with 
a radiated puncturing on the rest of the scale finer than in the D. macropygopterus. 
By its much smaller scales and head, and wider and shorter anal fin, this is fully distinguished from the 
D. macropygopterus with which Agassiz has united it. I have carefully verified these characters in several 
specimens, and feel satisfied that they are not the result of age or accidental injuries, as has been suggested. 
Position and Locality—Old Red sandstone. Abundant at Caithness. 
DIPTERUS MACROPYGOPTERUS (Sedg. and Murch.) 
Ref.—Sedg. and Murch. Geol. Trans. 2nd Series, Vol. III. Pl. 15. 
Desc—About nine inches long and nearly two inches deep behind the pectorals, from whence the body 
tapers gradually both towards the head and tail; head pointed, rather more than one-fourth the entire length ; 
upper lobe of the tail long, pointed; posterior margin very obliquely concayo-subtruncate ; posterior anal nearly 
reaching to the angle of the lower lobe of tail, narrower than the dorsal, exceeding by nearly one-third the 
depth of the body at its base; lateral line nearer to the dorsal than the ventral margin; scales nearly circular 
when detached ; those of the flanks three lines, and of the belly four lines in diameter, densely imbricated when 
in situ ; the height (diameter) being nearly three times greater than the length of the exposed portion; surface 
of each scale with strong imbricating concentric wrinkles on the exposed portion, the remainder being very 
minutely punctured and granulated in a close radiating manner. 
Position and Locality —Old Red sandstone. Common in the flags at Caithness. 
DirTerus VALENCIENNES (Sedg. and Murch.) 
Ref—Sedg. and Murch. Geol. Trans. 2nd Series, Vol. III. Pl. 16. fig. 1 and 3. 
Desc.—F usiform, depth greatest a little in front of the middle, being nearly one-fourth of the length, which 
varies from three to five inches; head small, pointed ; scales of the sides of the body scarcely one and half lines 
in diameter, two or three rows on the belly nearly double this size ; exposed portion when én situ about one-third 
