170 
SELACHI1. 
and Cochliodus \ and then naming others 1 2 . F. M‘Coy 3 described 
many species (some already bearing Agassiz’s MS. names), en¬ 
deavouring to show that Cochliodus itself was closely related to Pla- 
%/ 
coclus (now known to be a reptile), and, by mistaking a fragment of 
the inwardly coiled outer border, considered that the teeth succeeded 
vertically, as in the Pycnodonts 4 . In 1867 5 6 7 , P. Owen founded the 
family of Cochliodontidae, having already remarked 8 9 that “it would 
seem as if the several teeth of each oblique row in Cestrcicion had 
been welded into a single dental mass in Cochliodus , the proportions 
and direction of the rows being closely analogous.” About the 
same year, Newberry and Worthen \ described an American fossil 
proving the occurrence of small separate teeth together with the 
large plates in an ally of the British Cochliodus. In 1872, Hancock 
and Atthey 8 made known the presence of at least one dorsal fin- 
spine in the generalized genus Pleuroplcix (“ Pleurodus ”). In 1878 
and 1883, L. Gr. de Koninck°, J. W. Davis 10 11 , and St. John and 
Worthen u , added much to our knowledge of the detached dental 
plates; and still more recently, P. H. Traquair 12 has made known 
the greater part of the dentition of Psephodus, emphasizing its 
generalized character, besides pointing 13 to Pleuroplcix ( Pleurodus ) 
and Poecilodus as affording a clue to the true homologies of the 
larger teeth characterizing the whole family. 
It seems probable that the Cochliodontidae possessed two dorsal 
fins,' often provided with spines. In some beds, however, yielding 
Cochliodont teeth— e. g., those of Tieknall and Chapel-en-le-Frith 
(Derbyshire), Wensleydale (Yorkshire), and Beith (Ayrshire)— 
dorsal fin-spines are almost or quite unknown. 
The genera and species are distinguished by the form and pro¬ 
portions of the large “ dental plates ’’—morphologically, compound 
1 Tom. cit. pp. 104, 113 (1838). 
2 Tom. cit. p. 174 (1843). 
3 Bi’it. Palaeoz. Foss. (1855). 
4 Op. cit. p. 621. 
0 Geol. Mag. vol. iv. p. 59. 
6 Palaeontology, 2nd edit. (1861), p. 128. 
7 Palaeont. Illinois, vqI. ii. p. 89. 
8 Nat. Hist. Trans. Northumb. and Durham, vol. iv. p. 408. 
9 Faune Calc. Carbf. Belg. pt. i. (Ann. Mus. Roy. d’Hist, Nat. Belg. 
vol. ii.). 
10 Trans. Roy. Dublin Soc. [2] vol. i. (1883), pp. 327-600, pis. xlii.-lxv. 
11 Palaeont. Illinois, vols. vi., vii. 
12 Trans. Geol. Soc. Glasgow, vol. vii. (1884), p. 396, pi. xvi.; and Geol. 
Mag. [3] vol. ii. (1885), p. 340, pi. viii. 
13 Geol. Mag. [3] vol. v. (1888), p. 84. 
