550 
ACTIN' OPTERY GIT. 
remote, relatively large, with closely articulated rays; median fins 
large, with distinct fulcra, the rays with distant articulations and 
ornamented by longitudinal striae. Dorsal and anal fins arising at 
the dorsal and ventral gibbosities respectively, extending close to 
the origin of the caudal fin, much elevated in front, the maximum 
height of the dorsal equalling at least one-third the depth of the 
trunk at its origin. Scales of flank deep and rhombic, those dor- 
sally and ventrally and towards the end of the caudal region nearly 
equilateral; ornamentation consisting of very fine parallel striae, in 
the direction of the long axis of the principal flank-scales, but 
somewhat oblique on those above and below. 
Form. <$f Loo. Calciferous Sandstones (Cement-stone Group): 
Eskdale, Dumfriesshire. 
P. 4060. Imperfect typical specimen, wanting paired fins, in 
counterpart. Purchased , 1883. 
P. 4061. Small imperfect specimen, with remains of pelvic fins. 
Purchased , 1883. 
The following species have also been determined, but there are 
no examples in the Collection 
Plafysomus circularis, Newberry & 'Worthen, Pal. Illinois, vol.iv. 
(1870), p. 347, pi. iv. fig- 2.—Coal-Measures; Mazon 
Creek, Illinois. v 
Platysomus orlicularis, Newberry & Worthen, ibid. pi. iii. fig. 1 
(no description).-—Coal-Measures ; Illinois. v 
The so-called Platysomus jischeri, Arndt (Bull. Soc. Imp. Nat. 
Moscou, vol. xxiii. 1850, pt. i. p. 88, pi. i.), is founded upon the 
tail of a bony (probably physoclystous) Tertiary fish, from the 
neighbourhood of Simferopol. 
Of the remarkable Upper Permian genus Dorypterus (E. E. 
Germar, in Munster’s Beitr. Petrefakt. pt. v. 1842, p. 35) there are 
no examples in the Collection. This fish still requires satisfactory 
elucidation, but is evidently related to the Platysomatidae, as indi¬ 
cated by the great development of the azygous fin-supports, which 
are sometimes at least in part mistaken for dermal structures. So 
far as the absence of flank-scales is concerned, Dorypterus bears the 
same relation to the typical Platysomatidae as Phanerosteon with 
respect to the typical Palaeoniscidae. A single species is recognized 
thus :— 
Dorypterus lioffmanni , E. E, Germar, in Munster’s Beitr. Petre- 
