PLEFRACANTHIDJ3. 
3 
Aganoclus, Ochlodus, and Pternodus , according to Hancock and 
Atthey \ are supposed genera founded upon fragments of the teeth 
named Diplodus. Didymodus must also be included here until 
satisfactory evidence as to its true position is obtained; the dis- 
' tinctive features noted by Prof. Cope 2 are most probably due to the 
perfection of the Texas fossils as compared with those of Europe. 
The teeth of most species of Pleuracanthus cannot yet be corre¬ 
lated with the spines, and it is thus necessary still to retain the 
provisional name of Diplodus . 
I. Species already hnoion with much completeness „ 
Pleuracanthus decheni (Goldfuss). 
1847. Orthacanthus decheni, Goldfuss, Neues Jahrb. p. 404. 
1847. Orthacanthus decheni , Goldfuss, Beitr. vorw. Fauna Steink. p. 23, 
pi. v. figs. 9-11. 
1848. Xenacanthus decheni , E. Beyrich, Monatsb. Verh. k. Preuss. 
Akad. Wiss. p. 24. 
1849. Triodus sessilis, Jordan, Neues Jahrb. p. 843. 
1851-56. Xenacanthus decheni , F. Roemer, in Bronn’s Leth. geo^n. 
3rd ed. vol. i. p. 693, pi. ix 4 . fig. 15. 
1856. Xenacanthus decheni , Sclinur, Zeitschr. deutsck. geol. Ges, 
vol. viii. p. 542. 
1857. Xenacanthus decheni , F, Roemer, Zeitschr. deutsch. geol, Ges, 
vol. ix. p. 60. 
1857. Pleuracanthus decheni , Sir P. Egerton, Ann. Mag. Nat, Hist. [2] 
vol. xx. p. 423. 
1861. Xenacanthus decheni , H. B. Geinitz, Ilyas, p. 23, pi. xxiii. fig. 1. 
1867. Xenacanthus decheni , R. Kner, Sitzungsb. k. Akad. Wiss. Wien, 
vol. lv. pt. i. p. 540, pis. i.-x, 3 
1868. Xenacanthus decheni, C. Liitken, Geol. Mag. vol. v. p. 376. 
1880. Pleuracanthus decheni, J. W. Davis, Quart, Journ. Geol. Soc, 
vol. xxxvi. p. 321. 
1883. Pleuracanthus and Xenacanthus , C. Hasse, Neues Jahrb. vol. ii. 
p. 65. 
Type. Imperfectly preserved skeleton; Berlin Museum. 
A comparatively small species, the barbed spine not attaining a 
greater length than about 0-11 m. in the adult. Spine much 
compressed and flattened antero-posteriorly ; denticles thick, pointed 
but not hooked, placed in very close series upon each lateral margin. 
Principal cones of the dental crown compressed, smooth or slightly 
striated, with a slender intermediate denticle. 
1 Nat. Hist. Trans. Northumb. & Durham, vol. iii. p. 113. 
3 See detailed description in Proc. Amer. Phil. Soc. 1884, pp. 572-590, plate. 
3 This is the most exhaustive account of the genus and species yet published. 
