PSAMMODONTIDiE. 
91 
Family PSAMMODONTIDflE. 
An extinct family, imperfectly recognizable, being known only by 
remains of the dentition. As shown by the teeth, the two rami of 
the jaws were evidently placed in the same straight line—a fact 
probably indicating a much-depressed body, like that of the existing 
Rays. The teeth are flattened, more or less quadrate, and have the 
root the same size as the crown; the contour of the base of the root 
corresponds to that of the crown, and the attached surface exhibits 
only slight longitudinal striations. The dentition was originally 
arranged in one, two, or several longitudinal series, arched antero- 
posteriorly; and when there are two or more series, the correspond¬ 
ing rows of the opposite sides are symmetrical. The teeth of adjoining 
series are not exactly opposite each other, but slightly alternating. 
Genus COPODTJS* Davis (ex Agassiz MS.). 
[J. W. Davis, Trans. Roy. Dubl. Soc. [2] vol. i. 1883, p. 464.] 
Syn. Labodus, Agassiz MS., Davis, loc. cit. p. 468. 
Mesogo?jiphus, Agassiz MS., Davis, loc. cit. p. 470. 
Rhymodus, Agassiz MS., Davis, loc. cit. p. 473. 
Characodus, Agassiz MS., Davis, loc. cit. p. 474. 
Pinacodus, Agassiz MS., Davis, loc. cit. p. 476. 
Teeth bilaterally symmetrical, with the postero-lateral angles of 
the root, and sometimes also of the crown, much produced back¬ 
wards. They are narrower in front than behind, and the anterior 
margin is generally straight or convex. Coronal surface slightly 
rugose when unabraded, and generally almost flat, though in some 
cases upturned laterally; root about twice as thick as the crown. 
The teeth are especially characterized by the presence in each of a 
transverse sutural line, dividing a smaller or larger portion from the 
remainder, sometimes allowing of the complete separation of the 
parts, sometimes only faintly marked. 
The dentition of each jaw probably consisted only of a single 
antero-posterior series of teeth. 
The following is a provisional arrangement of the species, the 
number of which will doubtless be considerably reduced when more 
perfect specimens are known. 
Copodus corxmtus, Davis (ex Agassiz MS.). 
1843. Pscimmodus cornutus, Agassiz, Poiss. Foss. vol. iii. p. 174 (name 
only). 
