BEACHIOPODS. 75 



Leptaena sericea SOWKRBY. 



Plate xxxix, fig. 9. 



Leptasna se'icea Sowerby, 1839: 811. Spat., p xix, figs. 1-2. 

 Strophomena sericea Conrad, 1840: Geol. N"ew York, A.nn. Rep., p. 201. 

 Leptcena sericea Meek, 1873: Geol. Sur. Ohio, Pal., vol. I, p. 70, pi. 5, figs. 

 3a-h. 



Shell small, transverse, semi-oval, approaching semi-circu- 

 lar, concavo-convex : hinge-line equaling, or more frequently a 

 little longer than the breadth of the valves at any point farther 

 forward; lateral extremities varying from some what acutely an- 

 gular to nearly or quite rectangular, and not properly reflected ; 

 anterior and lateral margins forming together nearly a regular 

 semi-circle curve. Dorsal valve concave, its deepest concav- 

 ity being near the middle ; beak not distinct from the cardinal 

 margin ; area narrow or nearly linear, and ranging at right angles 

 to the plane of the valves. Interior showing cardinal margin 

 to be minutely crenulated toward the lateral extremities; car- 

 dinal process moderately prominent, and trifid, the middle di- 

 vision being most prominent, with a deep pit at its inner base ; 

 brachial ? process short, appressed, and widely divergent ; mus- 

 cular impressions generally obscurely defined, occupying an 

 obcordate area, and separated from each other by two sub- 

 parallel, narrow ridges that sometimes coalesce near the base 

 of the cardinal process ; each impression usually nearly equally 

 divided by a slender linear, straight ridge ; anterior and lateral 

 regions more or less roughened by minute granular radiating 

 stride. 



u Ventral valve moderately convex, being nearly evenly but 

 gently arched along the middle from beak to the front, and 

 thus following so nearly the curve of the other valve as to 

 leave but a very thin visceral cavity within; beak very small, 

 or scarcely if at all distinct from the cardinal margin ; area 

 twice or three times as high as that of the other valve, inclined 

 backward, or more or less nearly parallel to the plane of the 

 valves; foramen arched over near the beak by a- small false 

 deltidium, closed between this and the hinge margin by the 

 prominent cardinal process of the valve. Interior showing 



