Bulletin 24 56 



This species bears much resemblance to the common Miocene 

 B. mactroides. Its most distinguishing characteristic is the radial 

 plication. These plications are strong in full-grown shells but in 

 immature shells show only as broad crenulationsof the basal mar- 

 gin. B. virginiana is more elongated, more convex and with 

 a less polished surface. 



Yorktown formation ; Grove Wharf, Kingsmill, James riv- 

 er near Smithfield. 



Rochefortia (Pythinella) filicaticola n. sp., Plates, Fig's 10-12 



Shell small, elongated and with the anterior end much produ- 

 ced and one and a half times again as long as the posterior ; an- 

 tero-dorsal margin straight with the extremity evenly rounded ; 

 postero-dorsal margin curved behind the beak, becoming straight 

 posteriorly and terminating in the well-rounded posterior extre- 

 mity ; basal margin with a moderately deep insinuation pointing 

 towards the beak ; surface of shell with fine concentric growth 

 lines and with a few resting marks ; right valve with two promi- 

 nent thickened teeth, separated by a deep notch ; in the left valve 

 the notch is wider bordered by rather thin laminae formed by a 

 slight thickening and beveling of the valve margin. 



Length 3. 00, height 1.75 mm. 



The type specimen together with several specimens of the 

 same species were all found inside of a gasteropod shell belonging 

 to Latiurus filicahis Con. All the specimens had both valves in- 

 tact so that together with their peculiar shape, a commensal or 

 parasitic habit on the above mentioned gasteropod may be taken 

 for granted. In its hinge structure and shape, this species agrees 

 well with the recent Rochefortia cuneata Verrill and Bush which 

 is used by Dall as typifying the subgenus Pythinella. The Miocene 

 shells appear to differ from its recent representative, in having its 

 anterior end less elongated, anterior extremity more evenly round- 

 el and lastly in having the basal insinuation of its valves much 

 more pronounced. 



Yorktozan formation, James river, 5 miles north of Smith - 



Je'd, Va. 



