212 
SELACnll. 
By St. John and Worthen (Pal. Illinois, vol. vii. 1883), dental 
plates of the form of Streblodus are hypothetically assigned to Vdto- 
ptychius expamus, U. primus, I), wetchsmuthi, and 1). varsomknsis, 
and to various species of Cochliodus. Vulicmodus, Stenoj>terodus, and 
Chitonodus. Another dental plate forms the t}’po of Cochliodus 
ohliquus, St. John and Worthen {tom. cit. p. 12G, pi. vii. fig. 17) 
from the St. Louis Limestone of Missouri. 
Genus DELTOPTYCHIUS, Agassiz. 
[Morris & llobcrts {ex Agassiz, MS.), Quart. Journ. Geol. Soc. 
vol. xvdii. 18G2, p. 100 '.] 
Two posterior series of teeth in each jaw represented by a single 
triangular dental plate, with the coronal surface destitute of trans- 
verse ridges and furrows ; postero-latcral border much longer than 
the antero-lateral, and this about equal in length to the inner mar- 
gin. A large broadening ridge extends from the outer apex to the 
inner margin ; while the postero- lateral border is somewhat raised, 
and the antero-lateral abruptly ridged, thus giving the plate a 
twisted appearance. 
The dental plates of one jaw (presumably the lower) are much 
more irirolled than those of the opposing jaw. They are evidently 
the homologuos of the posterior pair of largo plates in Deltodus and 
Cochliodus-, and appearances are suggestive of there having been no 
fusion of the teeth immediately in front into a second smaller plate. 
By 8t. John and Worthen “ the dental plates here assigned to 
the lower jaw of Deltopti/ckius are considered as referable to I’oecil- 
odus, while the “ upper” plates are regarded as truly pertaining to 
the lower jaw of the genus under consideration. The true upper 
dental plates of DdtoptycMus are identified by the same authors 
with species of Streblodus. We prefer, however, to adopt the inter- 
pretation of M‘Coy ^ as amended by Davis ^ 
Deltoptychius acutus, M‘Coy. 
1843. Cochliodus acutus, L, Agassiz, Poiss. Foss. vol. iii. p. 174 (name 
only). 
* The name only is here mentioned and applied to the species previously 
described and figured by M'Cuy under (he name of Cochliodus acutus. The 
typo species being thus already well-defined in 1862, the generic name may be 
regarded as dating from that year. 
‘‘ Pal. Illinois, vol. vii. (1883), p. 92. 
^ Brit. Palteoz. Foss. p. 621. 
' Trans. Boy. Dublin Soc. [2] vol. i. p. 432. 
