1862.] POWRIE OLD RED SANDSTONE. 435 



Pteeichthts. — Several specimens of this genus have been disin- 

 terred of late, one of which, in the St. Andrews Museum, exhibits 

 a rather complete view of the form and arrangement of the dorsal 

 plates ; while another has the ventral plates so distinct, that, although 

 imperfect on one side, their form and arrangement can be very satis- 

 factorily ascertained. Sir Philip Egerton's most interesting paper 

 in vol. iv. of the Quart. Journ. Geol. Soc. has so fully exhausted 

 this genus, that I have little, if anything, to add to it. All the spe- 

 cimens which I have yet seen of this fish from Dura Den fully cor- 

 roborate the correctness of the views advanced in that paper ; the 

 principal peculiarity of the Dura Den species {Pt. hydrophilus) being 

 the great length and the slender form of its pectoral appendages, 

 these much exceeding in this respect any of the older-known species, 

 although in. turn outdone by the lately discovered Pt. macrocephalus 

 of the yellow sandstones of Farlow*. In Pt. hydrophilus these ap- 

 pendages are about equal in length to the body, ^o other species 

 of this fish is found in Dura Den. 



Platygnathus and Diplopteeus. — N'o vestige of these genera has 

 yet occurred to me in the many fish-bearing slabs from Dura Den I 

 have examined. Judging from the drawings given in Dr. Anderson's 

 * Monograph,' I have little doubt that what is there figured as Pla- 

 tygnathus was a fully developed tail of Holojotychius or Glyptolepis ; 

 and what is given as Diplojpterus was merely an imperfect and dis- 

 torted head of Glyptolwmus. 



Gltptopomus. — I have only seen one very imperfect specimen of 

 this genus, and thus can add nothing towards completing its resto- 

 ration. 



Gltptolepis. — Perhaps the most interesting result of the late ex- 

 plorations in Dura Den has been the discovery of the remains of a 

 fish seemingly belonging to this genus, as pointed out by Mr. Page. 

 The creature in this specimen appears to have been so doubled up 

 and twisted, that the head and shoulders lie very nearly at right 

 angles to the body. Its length appears to have been not much under 

 2 feet, with a depth, at its greatest diameter, of about 4 inches ; but, 

 from the twisted condition of the body, these can only be tolerably 

 near approximations. The body was of about equal thickness from 

 the pectoral region to nearly that of the anal and posterior dorsal 

 fins, and from thence it gradually tapered off to the caudal extremity. 

 The posterior dorsal and anal fins are opposite, and placed at less 

 than their length from the tail-fin. In this specimen, these and the 

 caudal fin are well preserved. The caudal fin has much of the di- 

 phycercal character, the under lobe only slightly exceeding the upper 

 in size. The posterior dorsal fin seems to have been obtusely lobate. 

 The exact position of the anterior dorsal is not well shown, from the 

 twisted condition of the fish ; sufiicient, however, is preserved to show 

 that it was placed far back on the body, less than its own length in 

 advance of the posterior. The remains of what might have been a 

 ventral, or more probably a pectoral fin, are also distinctly marked. 

 None of these are sufficiently entire to show the lobation, if, as seems 

 * Quart. Journ. Geol. Soc. toI. xviii. p. 103. 



VOL. XVIII. PART I. 2 G 



