168 GANOID FISHES OF THE CARBONIFEROUS FORMATION. 



the shoulder-girdle, in front of the dorsal fin, on the caudal body-prolongation : Phane- 

 rosteon, Traquair. 



(3) Scales may also disappear, except a patch on each side of the abdominal region 

 and a row of >-shaped scales supporting the lateral line canal: Elpisopholis, Smith 

 Woodward. 



Other Acipenseroid families include genera in which the body-scales are degenerate 

 u]) to total disappearance, e.g. Chondrosteus (fam. Chondrosteidae), Potyodon, Crossopholis 

 (fam. Polyodontidae). Or, as we find in Acipenser itself, the typical rhombic ganoid 

 scales may be displaced by scutes. But whatever may be the condition of the scales on 

 the body of the fish, those which clothe the termination of the prolongation of the body- 

 axis are always present and of the same contour. (See the arrangement in Cryphiolepis, 

 p. 105, text-figure 4 of this work.) 



Geological Position and Locality. — Not uncommon in the fish-beds of Lower Carboni- 

 ferous age (Calciferous Sandstone Series) exposed in the banks of the River Esk at 

 Glencartholra, near Langholm. 



The small, apparently scaleless fish described by A. Fritsch as Phanerosteon pauper 

 from the Lower Permian Gas-coal of Bohemia, is not proved to belong to this genus. 

 Certainly the "restored" figure which accompanies his description runs very wide of 

 the mark — the details of the head, vertebral axis and fins not resemblino; to any sufficient 

 extent the details of the corresponding structures in Ph. mirabile. 



Genus — Holurus, Traquair, 18S1. 



Generic Characters. — Fusiform : dorsal fin arising behind the middle of the back, 

 not acuminate in front, long-based, extending almost to the commencement of the tail- 

 pedicle ; anal fin with a shorter base than the dorsal ; caudal strongly heterocercal but 

 not bilobate, triangular, its rays gradually diminishing posteriorly; pectorals unknown ; 

 ventrals small, arising slightly in front of the dorsal. Fin-rays in no case dichotomised ; 

 fulcra absent. Scales rhomboidal, sculptured; a prominent row of median scales 

 between the occiput and the commencement of the dorsal fin. Teeth small, cylindro- 

 conical. 



The structure of the head is decidedly Palseoniscoid, with oblique suspensorium and 

 wide gape; superethmoidal prominence not largely developed. 



1. Holurus Parki, Traquair. Plate XXXVIII, figs. 1 — 6. 



Holuiujs Parki, Traquair. Trans. Eoy. Soc. Edinb., vol. xxx, p. 43, pi. iii, 



figs. 9—12. 

 — —A. S. Woodward. Cat. Foss. Fishes Brit. Mus., pt. ii, 1891, 



p. 520. 



