1887.] NATURAL SCIENCES OP PHILADELPHIA. 53 



cylindrical and approaches the subgenus Actaeonidea Gabb, from the 

 Tertiary of the West Indies. It lacks, however, the anterior 

 truncation of the collumella of Actaeonidea. 



XTnicardiuml eocenense n. sp. PI. Ill fig. 14, 14 a. 



Small, tumid, solid. Margin subquadrangular, rounded 

 anteriorly, truncate posteriorly. Beak turned anteriorly, before it 

 a small cordate lunule. Lunular edge in front of the beak somewhat 

 ex23anded. Below the beak one tubercular cardinal tooth (left valve), 

 lateral teeth nearly obsolete. Anterior muscular impression 

 elongated elliptical, posterior impression cordate-elliptical. Pallial 

 impression not entire. Inside rough. Margin entire. Surface with 

 indistinct concentric impressed lines, crossed by more distinct 

 radiating lines. This ornamentation is wanting on the umboneal 

 part and more distinct near the margin. The radiating lines are 

 slightly more distinct on the posterior slope. Red Bluff, 3fiss. 



The only found specimen, a left valve, shows three sinuations of 

 the pallial line behind. I have little doubt that this species belongs 

 either to Unicardium d'Orbigny, or Fimhriella Stoliczka, or is to be 

 placed in their neighbourhood. These two genera, however, are not 

 knowai from the Tertiary formation, and if the Red Bluff form 

 should prove to be a diffp-vent and new genus I j^roiwse the name of 

 Cordiula for it. 



MIKROLA n. gen. 



Minute, subtrigonal, inaequilateral. Anterior side rounded, 

 posterior side attenuated. Ligament in a trigonal pit below the 

 beak. In the right valve this pit is lodged between two compressed 

 cardinal teeth. Left valve without distinctly developed teeth. 

 Muscular impressions oval? Pallial line sinuated behind. Surface 

 concentrically ribbed. Margin entire. 



At first sight the genus has much resemblance to Spheniojysis, 

 Sandberger, especially the left valve. But the dentition of the right 

 valve is entirely different, and the genus may even not belong to the 

 Myidae. I cannot discover any gaping of the valves. 



Mikrola mississippiensis n. sp. PI. Ill fig. 16, 16a, 16b. 



Beaks almost obsolete. The concentric ribs of the surface end at 

 the posterior terminal slope. IJmbonial part smooth. 



Red Bluff, Miss. 



I found three double-valves of this species, which varies very 

 iQuch in the size and number of the concentric ribs. While one 



