PALEONTOLOGY OF IOWA. 657 



BRACHIOPODA OF THE WARSAW LIMESTONE. 



IN the exposures of this rock along the Mississippi river, 

 in Iowa and the adjacent parts of Illinois, comparatively 

 few species of Brachiopoda are usually observed. In the 

 more southern localities, however, these forms become more 

 numerous ; and in the continuation of this rock in Indiana, 

 there are a considerable number of species known ; most of 

 them, however, of small size, and associated with nume- 

 rous species of Lamellibranchiata and Gasteropoda. I have 

 selected from all those known to me from the different lo- 

 calities, such as appear to be most characteristic of the 

 formation. 



Retzia verneuilana. 



PLATE XXIII. FIG. 1 a, b, c, d. 

 Retzia verneuilana : HALL, Transactions of the Albany Institute, Vol. 4, 1856. 



SHELL longitudinally ovate : valves almost equally convex. 

 Ventral valve most prominent near the beak, which is ele- 

 vated and incurved so as to bring the circular foramen nearly 

 on a line with the margins of the valves : foramen round. 

 Dorsal valve smaller, auriculated on the cardinal angles : 

 beak small, scarcely rising above the straight cardinal mar- 

 gin ; area small, triangular, not entirely confined to the 

 larger valve, bounded by a distinct angular margin. 



SURFACE longitudinally striate, marked by about fifty 

 rounded, beautifully punctate, simple strise. 



Length, '10 to -32, width 08 to -27 of an inch, usually. 

 Some specimens have a length of three-fourths of an inch. 



Fig. 1 a, b. Ventral and dorsal views of a small individual. 



Fig. 1 c. An enlarged figure, showing the foramen and auriculate extensions of the 

 dorsal valve. 



Fig. 1 d. Enlarged figure of the same. 



Geological formation and localities. In limestone of the age of the War- 

 saw limestone : Spergen hill and Bloomington, Iowa. 



[ IOWA SURVEY.] 83 



