170 
SELACmi. 
and Coehliodus and then naming others F. M‘Coy ^ described 
many species (some already bearing Agassiz's iMS. names), en- 
deavouring to show that Coehliodus itself was closely related to Pla- 
endus (now known to bo a reptile), and, by mistaking a fragment of 
the inwardly coiled outer border, considered that the teeth succeeded 
vertically, as in the Pycnodonts In 1807°, It. Owen founded the 
family of Cochliodontidae, having already remarked “ that “ it would 
seem as if the several teeth of each obli(jue row in Ceslracion had 
been w'eldcd into a single dental mass in Cocldiodus, the proportions 
and direction of the rows being closely analogous.” About the 
same year, Newberry and AVorthen described an American fossil 
proving the occurrence of small separate teeth together with the 
large plates in an ally of the British Cocldiodus. In 1872, Hancock 
and Atthcy * made known the presence of at least one dorsal fin- 
spine in the generalized genus Pleuroph.v (“ Pleurodus ”). In 1878 
and 1883, L. 0. do Koninck”, J. W. Davis'", and St. John and 
Worthen ", added much to our knowledge of the detached dental 
plates ; and still more recently, R. II. Traquair has made known 
the greater part of the dentition of Psephodus, emphasizing its 
generalized character, besides pointing to Pleuroplax {Pleurodus) 
and Pmilodm as affording a clue to the true homologies of the 
larger teeth characterizing the whole family. 
It seems probable that the Cochliodontida) possessed two dorsal 
flns, often provided with spines. In some beds, however, yielding 
Cochliodont teeth — e. g., those of Ticknall and Chapcl-eu-le-Frith 
(Derbyshire), AVensleydalo (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 
‘ Tom. ait. pp. 104, 113 (1838). 
= Tom. cU. p. 174 (1843). 
’ Brit. I’alaioz. Foss. (185.')). 
■* Op. cit. p. 621. 
Gleol. Mug. Tol. iv. p. .59. 
“ Palseontology, 2nd edit. (1801), p. 128. 
Balajoiit. Illinois, toI. ii. p. 89. 
" Nat. Hist. Trans. Northiimb. and Durham, vol. iv. p. 408. 
* Faune Calc. Carbf. Belg. pt. i. (Ann. Miis. Roy. d’llist. Nat. Bclg. 
vol. ii.). 
Trans. Roy. Dublin Soc. [2] vol. i. (1883), pp. 327-600, pis. xlii.-Ixv. 
" PaliEont. Illinois, rols. vi., vii. 
Trans. Geol. Soc. Glasgow, vol. vii. (1884), p. 396, pi. xvi. ; and Geol. 
Mag. [3] vol. ii. (1885), p. 340, pi. viii. 
‘3 Geol. Mag. [3] vol. r. (1888), p. 84. 
