46 
SELACHII. 
the homologous parts of the latter are misinterpreted, the apical 
edge being regarded as the anterior coronal margin, and the pos¬ 
terior half of the coronal face as a portion of the root. It must, 
however, be admitted that at this point there is no very philoso¬ 
phical line of distinction between the teeth named Helodus and the 
Petalodonts. 
Form. Sf Log. Lower Carboniferous (Bone-bed in Lower Limestone 
Shales): Bristol, England. 
P. 2652. Eour teeth; Bristol. One of these specimens is unsym- 
metrical, evidently having been laterally placed. 
Enniskillen Coll. 
P. 1464. Three teeth; Bristol. Egerton Coll. 
Petalodus davisii, sp. nov. 
Type. Detached teeth; British Museum. 
Teeth extremely elongated, very similar to those of P. rectus, but 
somewhat smaller and even longer in proportion to their height; 
coronal surface with numerous vertical wrinkles and a tendency 
towards crenulation of the margin; root considerably crimped. 
Form. Sf Log. Lower Carboniferous Limestone : Armagh, Ireland. 
P. 2656 a, P. 2656. Two type specimens and sixteen similar teeth. 
Enniskillen Coll. 
P. 1463. Similar imperfect tooth ; Armagh. Egerton Coll. 
A larger imperfect tooth (P. 5456) from the Lpper Carboniferous 
Limestone of Bichmond, Yorkshire, seems to indicate a species allied 
to the foregoing ; and another fragmentary tooth (P. 2913, Ennis¬ 
killen Coll.), from the Lower Carboniferous Limestone of Armagh, 
has been described by Davis (Trans. Boy. Dublin Soc. [2] vol. i. 
1883, p. 509, pi. lxi. fig. 2) under the name of Chomatodus acutus . 
C S iC A) 
Petalodus allepjlianiensis, Leidy. 
1856. Sicarius extinctus, J. Leidy, Proc. Acad. Nat. Sci. Philad. vol. vii. 
p. 414. 
1856. Petalodus alleghaniensis, J. Leidy, Journ. Acad. Nat. Sci. Philad. 
[2] vol. iii. p. 161, pi. xvi. figs. 4-6. [Specific name, extinctus, 
withdrawn.] 
1866. Petalodus destructor, J. S. Newberry & A. H. Worthen, Pal. 
Illinois, vol. ii. p. 35, pi. ii. figs. 1-3. 
1870. Petalodus destructor, 0. St. John, Proc. Amer. Pliil. Soc. vol. xi. 
p. 433. 
