PLATE IV c— Continued. 

 MONOMERELLA EgANI, Sp. IIOV. 



Fig. 16. A brachial valve ; showing the strongly developed cardinal ai-ea, the narrow crescent and the 

 ■jilatform scars. The umbgnal cavity is filled by a thick dejiosit of testaceous matter. 

 Niagara limestone. Qrafton, Wisconsin. 



MoNOMEEELLA ovATA, vaf. LATA, AA^'hiteavcs. 



Fig. 17. The bi'achial side of an internal cast, believed to belong to this vai-iety. The umbonal cavity is 

 broad but well defined, the crescent and platform scai-s strongly developed. The three divei'g- 

 ing furrows in front of the platfoi-m are pi-obably to be regarded as vascular markings. 



Fig. 18. The opposite side of the same specimen ; showing the very short umbonal chambers. 

 Niagara limestone. Hawthorne, Illinois. 



