514 bulletin: museum of comparative zoology. 



raise the question whether all the specimens under discussion should 

 be considered one species. 



Locality: — Eden, Cincinnati, Ohio; Richmond (Maquoketa) at 

 Clermont, Iowa. 



Leptaena unicostata (Meek and Worthen). 

 Plate 2, fig. 5. 



Leptaena (n. sp.?) Owen, Geol. surv. Wisconsin, Iowa, Minnesota, 1852, pi. 



2B, fig. 3. 

 Strophomena unicostata Meek and Worthen, Geol. surv. Illinois, 1868, 3, p. 



335, pi. 4, fig. 11. Whitfield, Geol. Wise, 1882, 4, p. 262, pi. 12, fig. 14. 

 Rafinesquina imicostata Hall and Clarke, Pal. N. Y., 1892, 8, pt. 1, pi. 15A, 



fig. 39, pi. 20, fig. 25. 

 Leptaena unicostata Winchell and Schuchert, Geol. Minn., 1893, 3, pt. 1, p. 



411, pi. 32, fig. 6-9. Whiteaves, Pal. foss. Canada, 1897, 3, pt. 3, p. 174. 



This form occurs plentifully on thin slabs of limestone at the very 

 top of the Ordo\'ician in the Maquoketa at Patterson's Spring, near 

 Brainerd, Iowa. The specimens lack any sign of the wrinkling present 

 in some of the examples from Spring Valley, Minnesota. This species 

 can be distinguished from the American form now called Leptaena 

 tenuistriata Sowerby by the obsolete wrinkling, the large mid-rib and 

 the large bilobed diductor scars of the pedicle-valve. Strophomena 

 nitens Billings, an Anticostian form, closely resembles L. unicostata 

 exteriorly but not interiorly. 



Locality: — Richmond; Savannah, and Wilmington, Illinois; Dela- 

 field, Wise; Spring Valley and Granger, Minn.; Lattners, Brainerd, 

 Iowa; Rapids of Nelson River, Lake Winnipeg, Manitoba; Texas, 

 etc. M. C. Z. 8,546. 



