FROM THE CRETACEOUS FORMATION OF NEBRASKA. 387 



about 145 ; anterior side somewhat extended and regularly rounded ; posterior side 

 extended (and probably subtruncated). Shell marked by strong undulations, which 

 are simple at their extremities, while some of them become divided towards the centre 

 of the shell, where they are prominent, being less conspicuous towards the beak, and 

 almost obsolete towards the base of the shell. Concentric lines mark the surfaces of 

 exfoliated specimens somewhat irregularly. 



This species differs from the I. sagensis in the less obliquity of the form, and the 

 greater extension of the anterior side of the shell, giving an angle with the hinge line 

 of 50 greater than in that species. The concentric undulations in I. sagensis are 

 more simple than in this species, and more persistent towards the base of the shell, 

 while this is more ventricose in the middle. This shell appears to differ sufficiently 

 from all described species known to us, to render it easily recognizable. 



Locality and Position. Sage Creek. Upper part of division No. 4 of Section. 



INOCERAMUS TENUILINEATUS, n. sp. 

 PLATE II. FIG. 3, a, I. 



Shell obliquely rhomboid-ovate, height a little more than two thirds the length ; 

 beaks towards the anterior extremity, elevated, ventricose, and incurved; hinge line 

 straight, making an angle with the anterior margin of about 100; posterior side ex- 

 tremely elongated and rounded at the extremity; surface marked by irregular undula- 

 tions, which are nearly obsolete on exfoliated specimens. A small portion of the external 

 surface remaining near the anterior extremity, shows minute crowded concentric striae. 



This shell has the form and obliquity of I. sagensis, but the beaks are more elevated 

 and incurved, and the umbonial region more ventricose, while the undulations are much 

 less conspicuous, irregular, and more obtuse. The portion of the external surface 

 observed has the strise much finer and more closely crowded than in /. sagensis. This 

 species resembles in form the J. impressus of D'Orbigny, (Terrains Cretaces, p. 515, pi. 

 409,) except in the extension of the hinge line, which we have not been able to see in 

 its perfect condition. 



Locality and Position. Sage Creek and Great Bend of the Missouri. Division No. 

 4 of Section. 



INOCERAMUS CONRADI, n. sp. 



PLATE II. FIG. 5, a, I. 

 Shell very thin, ventricose ; surface marked by numerous fine concentric stria3 or 



