410 APPENDIX E. — PALEONTOLOGY. 



Fig. 4 b, the dorsal valve of a larger individual, having six pli- 

 cations on each side of the mesial sinus. 



The surface is marked by distinct, undulating, concentric striae, 

 which are again crossed by finer thread-like elevations, and which 

 appear to have been the bases of short spines. 



Loc. Missouri River, near Weston. 



Spirifer triplicata, Hall, (n. sp.) 



Plate II. Fia. 5 a b c. 



Shell subquadrangular ; dorsal valve more gibbous than the ven- 

 tral ; area nearly linear ; beak of dorsal valve small, acute, and 

 closely incurved ; mesial depression shallow in the upper part, but 

 becoming deeper and expanded toward the base, and produced in 

 front; entire surface, including the mesial sinus and elevation, 

 covered with fine plications, which, being simple in their origin, 

 soon divide into three, which are continued to the base without 

 further division. 



This species differs from the S. striatus, Sowerby, in its form, 

 and in the circumstance that the plications are less subdivided 

 toward the margin of the shell. 



Fig. 5 a, ventral valve, and area of the dorsal valve. 



Fig. 5 b, dorsal valve of the same individual. 



Fig. 5 c, profile view of the same. The form is somewhat dis- 

 torted by pressure. 



Loc. Missouri River, above Weston. 



Chonetes variolata, (D'Orb. sp.) De Koninck. 

 Plate III. Fig. lab. 



This species bears the essential characteristics of those figured 

 and described by De Koninck, though it is larger than most of his 

 figures. The broad, scarcely defined mesial depression of the 

 dorsal valve gives a straight or slightly sinuous outline in front. 



This fossil is associated with several of the preceding species, 

 near Weston on the Missouri River. 



