280 Syste.matic Paleontology — Middle Devo.viax 



Class GASTROPODA 



Subclass STREPTONEURA 

 Order ASPIDOBRANCHIA 



Suborder RHIPIDOGLOSSA 

 Family PLEUROTOMARllDAE 



Genus PLEUROTOMARIA Defrance 

 Subgenus BEMBEXIA Oehlert 



Pleuhotomaeia (Bembesia) sulcomarginata Conrad 

 Plate XXXA^, Figs. 1-5 



Pleurotomaria suJconiarginata Conrad, 1842, Jour. Acad. Nat. Sci., Phila., 



vol. viii, p. 2T2, pL xvi, fig. 13. 

 Pleurotomaria sulcomarguiatn Hall, 1862, Fifteenth Rep. N. Y. State Cab. 



Nat. Hist., p. 46, pi. v, figs. 9, 10. 

 Pleurotomaria sulcomarginata Hall, 1879, Pal. N. Y., vol. v, pt. ii, p. 69, pi. 



xix, figs. 8-17. 

 Bembexia sulcomarginata iririch and Scofield, 1897, Geol. Minn., vol. iii, pt. il, 



p. 955. 

 Bembexia sulcomarginata Grabau and Shimer, 1909, N. Am. Index Fossils, 



vol. i, p. 647, flg. 883. 



Description. — " Shell depressed trocliiform; spine moderately elevated; 

 apex minute; volutions four or five, ver}- depressed convex on the upper 

 side, gradually enlarging to the last one which becomes somewhat ventri- 

 cose; aperture subquadrate, somewhat wider than high, the columella 

 much extended below. Surface marked by two distinct, narrow, revolving 

 carinae on each volution, one just below the suture, and the other near 

 tlie periphery, with finer intermediate striae which are rarely visible; the 

 entire surface marked by strong, regular and even concentric striae which 

 crenulate the revolving carinae, and, passing over the lower one, bend 

 backward to the concave peripheral band; suture sometimes sharply canal- 

 iculate." Hall, 1879. 



A considerable numl)er of fairly large and smooth, with the exception 

 of a convex band about the periphery of the last whorl, internal impres- 

 sions occur in the Hamilton beds of Maryland and the adjacent part of 



