PLATE IV c—Continued. 
Monomekella Egani, sp. nov. 
16. A brachial valve; showing the strongly developed cardinal area, the narrow crescent and the 
platform scars. The umbonal cavity is filled by a thick deposit of testaceous matter. 
Niagara limestone. Grafton, Wisconsin. 
Monomerella ovata, var. lata, Whiteaves. 
17. The brachial side of an internal cast, believed to belong to this variety. The umbonal cavity is 
broad but well defined, the crescent and platform scars strongly developed. The three diverg¬ 
ing furrows in front of the platform are probably to be regarded as vascular markings. 
18. The opposite side of the same specimen; showing the very short umbonal chambers. 
Niagara limestone. Hawthorne, Illinois. 
