182 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



STREBLODUS Auassiz. 



Streblodua 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 3, Fig. 20, Text-flgure 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- 



Streblodus angustus, .^^g ^^ ^^^ antero-lateral margin. 



T t 1 1 t V 1 '^^® posterior dental plate upon which this species is 



founded has a total length of 2 cm., and width in the 

 middle portion of 7 mm., 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. 



Helodus rugOSUS Newberry and Worthen. 



(Plate 3, Fig. 14.) 



1870. Helodus rugosus Newberry and Worthen, Pal. Illinois, Vol. IV., p. 359, PI. 

 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. VII., 1883, p. 92. 



2 Cat. Foss. Fishes Brit. Museum, Pt. i., 1889, p. 212. 

 8 Brit. Palaeoz. Foss., 1855, p. 621. 



4 Trans. Roy. Dublin Soc. (2), Vol. I., 1883, p. 432. 



