354 Repoet of the State Geologist. 



Length of the original specimen, 9 mm.; width along hinge- 

 line, 10 mm. 



Upper Devonian. Rookford, Iowa. 



Strophonella costatula. 



Plate 6, figs. 9, 10. 



Strophonella costatula, Hall. Palaeontology of N. Y., vol. VIII, pt. 2, p. 



359, pi. Ixxxiv, figs. 15, 16. 1894. 



Shell subsemicircular in outline; hinge-line straight or slightly 

 arched ; surface depressed concavo-convex. 



Pedicle-valve elevated at the beak, becoming rapidly depressed 

 anteriorly, the median depression continued upon the short lin- 

 guiform extension at the anterior margin. Corresponding to 

 this depression is a broad anterior fold on the opposite valve. 

 The surface of both valves is covered with a few coarse, round, 

 sharply elevated ribs, which rapidly bifurcate or multiply by 

 implantation. These are more or less irregular or sinuous, ele- 

 vated at the concentric varices and crossed by faint concentric 

 lines. 



The typical example has a length of 21 mm., and a width on 

 the hinge of 24 mm. 



Niagara group. Louisville, Ktntucky. 



Plectambonites producta. 



PlateG, figs. 11, 12. 



Plectamho rates producta, Tl&ll. Palaeontology of N. Y., vol. VIII, pt. 2, p. 



360, pi Ixxxiv, figs. 23, 24, 25. 1894. 



The original of this species is an internal cast of the pedicle" 

 valve, with short, straight hinge ; rather narrow, depressed 

 umbo, the shell becomiDg" highly convex and greatly produced 

 anteriorly. The sides of the valv^e are somewhat appressed 

 medially and the anterior margin slightly expanded and suboval 

 in outline. The cast shows the impression of short, divergent 

 dental plates and a moderately broad muscular impression. The 

 width of the shell on the hinge is 10 mm ; its length, 23 mm ; its 

 convexity from the posterior margin, 8 mm.; from the anterior 

 margin, 23 mm. 



Niagara dolomites. Yellow Springs, Ohio. 



