212 SF/LAcim. 
By St. John and Worthen (Pal. Illinois, vol. vii. 1883), dental 
plates of the form of Streblodus are hypothetically assigned to Delto- 
ptychius expcinsus , D. primus, D. wacJismuthi, and D. varsouviensis, 
and to various species of Cocliliodus. Vaticinodus , Stenopterodus , and 
Chitonodus. Another dental plate forms the type of Cocliliodus 
obliquus , St. John and Worthen (tom. cit. p. 126, pi. vii. fig. 17) 
from the St. Louis Limestone of Missouri. 
Genus DELTOPTlfCHXUS, Agassiz. 
[Morris & Roberts (ex Agassiz, MS.), Quart. Journ. Geol. Soc. 
vol. xviii. 1862, p. 100 h] 
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-lateral 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 inrolled than those of the opposing jaw. They are evidently 
the homologues of the posterior pair of large plates in Deltoclus and 
Cocliliodus ; and appearances are suggestive of there having been no 
fusion of the teeth immediately in front into a second smaller plate. 
By St. John and Worthen 1 2 the dental plates here assigned to 
the lower jaw of Deltoptycliius are considered as referable to Poecil- 
oclus , while the ee upper” plates are regarded as truly pertaining to 
the lower jaw of the genus under consideration. The true upper 
dental plates of Deltoptycliius are identified by the same authors 
with species of Streblodus. We prefer, however, to adopt the inter¬ 
pretation of M‘Coy 3 as amended by Davis 4 . 
Beltoptychius acutus, M‘Coy. 
1843. Cocliliodus acutus , L. Agassiz, Poiss. Foss. vol. iii. p. 174 (name 
only). 
1 The name only is here mentioned and applied to the species previously 
described and figured by M'Coy under the name of Cocliliodus acutus. The 
type species being thus already well-defined in 1862, the generic name may be 
regarded as dating from that year. 
2 Pal. Illinois, vol. vii. (1883), p. 92. 
3 Brit. Palaeoz. Foss, p, 621. 
1 Trans. Roy. Dublin Soc. [2] vol. i. p. 432. 
