182 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 
STREBLODUS Aeassiz. 
Streblodus may be conveniently retained as a provisional genus in the sense 
intended for its employment by Agassiz. A different interpretation has been 
suggested by St. John and Worthen,! who distribute the dental plates referred 
to Streblodus amongst the genera Cochliodus, Deltoptychius, and Chitonodus, 
but confirmation of their views by direct evidence is lacking. The same may 
be said regarding their theoretical reconstruction of the dentition in Deltopty- 
chius, and we agree with Woodward? and others in preferring to adopt the 
interpretation of M’Coy ° as amended by Davis.* 
Streblodus angustus, sp. nov. 
(Plate 2, Fig. 20, Text-figure 9.) 
Type. — Posterior dental plate ; Museum Nebraska State University. 
Definition. — Posterior dental plate narrow and elongate, obliquely truncated 
in front, outer margin broadly arched, and postero-lateral border forming an 
acute angle with the inner margin. Posterior tumid por- 
tion of coronal surface sharply separated by an abrupt 
elevation from the anterior portion, and exceeding the 
latter in extent. Anterior portion crossed by a narrow, 
angulated, and very oblique ridge, with a slight thicken- 
ing of the antero-lateral margin. 
The posterior dental plate upon which this species is 
founded has a total length of 2cm., and width in the 
middle portion of 7mm., the form being quite narrow and antero-posteriorly 
elongated as compared with other species. It bears a rather remote resem- 
blance to S. obliquus (St. J. and W.) from the St. Louis limestone of Mis- 
souri, but is more attenuated and lacks the prominent fold along the 
antero-lateral border. 
Formation and Locality. — Atchison shales (Missourian); South Bend, 
and Cedar Creek, Nebraska. 
Fia. 9. 
Streblodus angustus, 
sp.nov. Posterior 
dental plate, X }. 
Helodus rugosus Newserry and WorrHen. 
(Plate 2, Fig. 14.) 
1870. Helodus rugosus Newberry and Worthen, Pal. Illinois, Vol. IV., p. 359, Pl. 
II., Fig. 10. 
A detached tooth obtained by Professor Barbour from the Missourian of 
Table Rock, Nebraska, exhibits all the characters described for this species, 
1 Pal. Illinois, Vol. VIL. 1883, p. 92. 
2 Cat. Foss. Fishes Brit. Museum, Pt. i., 1889, p. 212. 
3 Brit. Palaeoz. Foss., 1855, p. 621. 
4 Trans. Roy. Dublin Soc. (2), Vol. I., 1883, p. 432. 
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