1870.] '^'^* [Ifayden. 



the tooth becomes exceedingly thin, and in the specimen before me tlie 

 pointed end and outer margin are broken away. The superior surface is 

 coarsely punctate, as is also the straight articular margin. Distance be- 

 tween the angles of the broader extremities .38 inch. 



The tooth above described possesses some characters which seem to 

 connect it more closely with Xystrodus, Agassiz, (MS.) than with any 

 other genus with which I am acquainted. Its general depressed tritu- 

 rating surface, and but slightly convoluted terminal extremity, are strongly 

 suggestive of this relation. The genus Xystrodus was established by 

 Prof. Agassiz, for the reception of Cocliliodus striatus and two or more 

 other European species from the moiintain limestone. 



Form, and Loc. — Upper Coal Measures. 



Deltodus? angularis, N. and W. 



iZef.— Newberry and Worthen, Geol. Illinois, Vol. II, p. 97; PI. IX, Fig. 1. 



Description. — Terminal tooth small, obliquely triangular in outline, 

 thick, but slightly inroUed; the broader extremity has a sigmoidal curva- 

 ture terminating in an acute point at the oblique posterior extremity; 

 straight side forming an angle of about 55° with the oblique margin, ab- 

 ruptly truncated, with a narrow sulcus about the middle of the beveled 

 articular face extending from the inner angle to the pointed end, below 

 which the tooth apparently expands into a thin narrow border similar to 

 that upon the opposite side; the articular margin is bordered by a promi- 

 nent flattened ridge which occupies about one-third the surface of the 

 crown and gradually narrowing as it ajiproaches the terminal point; a 

 sharp, narrow keel rises from the oblique margin, rapidly converging and 

 decreasing in prominence toward the apical end, and separated from the 

 broad, flattened prominence of the straight margin by an equally broad, 

 deep, angular furrow; along the oblique side the tooth was slightly ex- 

 panded into a thin marginal border. The crown surface is beautifully 

 granulo-punctate, the broader extremity very faintly marked by longitu- 

 dinal sigmoid lines of growth, and the broad mesial depression is traversed 

 by very obscure undulations parallel with the oblique keel. Under sur- 

 face longitudinally undvilated, smooth. 



Length of tooth along the straight margin, about .53 inch.; greatest 

 distance between the acute and obtuse angles of the broader extremity, 

 .48 inch. 



The collection affords but a single example of this handsome form. The 

 specimen before me has a remarkable resemblance to the posterior teeth 

 of BeUopiycJiius Agassiz (M3.), founded upon Cochliodus acutus, of the 

 Irish mountain limestone, but we do not at present possess the materials 

 fully to demonstrate this identity. The Nebraska tooth, however, is evi- 

 dently identical with the form described by Messrs. Newberry and Wor- 

 then, from stratigraphically corresponding horizons in Illinois; and Dr. 

 AVhite has discovered the same, or a very closely allied species, in the 

 Upper Coal Measures of southwestern Iowa. 



Form, and Loc. — Upper Coal Measures. 



A. P. S. — VOL. XI. — 27e 



