228 Observations upon the Geolog'p and Paleontology 



give sharpness to the angle, and also, by slight lateral 

 projection in front of the cardinal teeth, gave security to 

 the hinge. Length from four to five lines, breadth from 

 five to six lines. 



Geological formation and locality. In the lower portion 

 of bed No. 7 of the preceding sections, Burlington, Iowa, 

 where it is rare. 



The discovery of a species of this interesting genus, 

 established by Prof. Plall in 1857, at the base of the Car- 

 boniferous system, materially extends the known geologi- 

 cal range of the genus. 



Dedicated to the Rev. W. H. Barris, rector of Christ 

 Church, Burlington, Iowa. 



TEREBRATULA BURLINGTONENSIS (White.) 



Shell rather small, longitudinally oval, gibbous or slightly 

 compressed, broadest a little forward of the middle. 



Ventral valve regularly convex, beak large, projecting 

 considerably beyond the dorsal valve, incurved. 



Hinge-line abruptly curved, deltidium in two pieces, 

 truncated at the apex by the foramen, concave at the base 

 to receive the beak of the dorsal valve. A faint, scarcely 

 defined ridge on each side of the beak follows its curva- 

 ture from the foramen, and finally loses itself at the mar- 

 gin, near the middle of the shell. 



Dental plates strong, deep, and nearly perpendicular, 

 bevelled backward, and presenting a sharp edge in front, 

 tapering and projecting slightly above the margin. 



Dorsal valve depressed convex, forming a sinuate junc- 

 ture with the opposite valve at the sides of the shell, a little 

 the most convex near the beak. 



Beak broad, not incurved. Cardinal process consisting 

 simply of a small projecting rim around the inside of the 

 hinge-line, the ends of which incline inward from the mar- 



