BRACHfOPODA. 231 



1908. Rhipidomella musculosa Clarke, Mem. N. Y. State Mus., vol. 9, pt. 1, p. 201, 



pi. 42, figs. 1-5; pi. 43, figs. 14, 17, 19, 20, 22. 

 1913. Rhipidomella musculosa Schuchert, Geol. Surv., Md. Low. Dev., p. 305, pi. 55, 

 fig. 20; pi. 56, figs. 1-4. 



Description- — Shell attaining a rather large size in mature examples, slightly broader 

 than long. The dimensions of an average sized individual are: Length 35 to 36 mm., 

 width 37 mm. Suborbicular in outline, hinge line short. 



Pedicle valve depressed convex, flattened towards the anterior and lateral margins 

 from the umbonal region. Beak small and slightly incurved above the hinge line. The 

 muscular scars are strongly developed, large, fan-shaped, and extend well beyond the 

 middle of the shell. Pallial region prominent. 



Brachial valve much more convex than the pedicle, the surface sloping gently toward 

 the lateral margins, and more abruptly toward the anterior margin. 



Surface of both valves marked by fine radiating costae about 3 occupying the 

 space of 1 mm. Concentric lines of growth also cross both valves, and appear to be 

 more prominent on the pedicle valve, especially near the anterior margin. 



Remarks — This is one of the less common species of the fauna, and all the speci- 

 mens examined are separate valves. 



Horizon— Lower and upper beds. 



Figured specimens No. 27479 Walker Museum. 



Superfamily Strophomenacea 

 Family Strophomenidae 

 Genus Leptaena Dalman 



Leptaena ventricosa (Hall) 

 Plate 61, figures 15-17. 



1857. Strophomena depressa var. ventricosa Hall, Tenth Ann. Rept. N. Y. State Cab. 



Nat. Hist., p. 55. 

 1859. Strophomena rugose var. ventricosa Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 417, 



pi. 94, figs. 2e, 2f, 3. 

 1892. Leptaena rhomboidalis var. ventricosa Hall and Clarke, ibidem, vol. 8, pt. 1, 



pi. 15a, fig. 43. 

 1908. Leptaena rhomboidalis var. ventneosa Clarke, N. Y. State Mus., Mem. 9, pt. 2, 



p. 87, pi. 21, fig. 87. 

 1913. Leptaena rhomboidalis var. ventricosa Schuchert, Geol. Surv., Md. Low. Dev., 



p, 309, pi. 56, fig. 18; pi. 57, fig. 1. 

 Description — Shell semi-circular to semi-oval in outline, sometimes attaining 

 large size. Width commonly somewhat greater than the length, but in some examples 

 the dimensions are nearly equal. The hinge line is equal to the greatest width of the shell, 

 and the extremities are extended into conspicuous auricular projections in some cases. 

 The dimensions of the pedicle valve of a large individual are: Length 39 mm., width 

 40 mm. A smaller shell measures 32 mm. in length and 34 mm. in width. 



Pedicle valve extremely ventricose, the greatest convexity anterior to the middle 

 of the shell, and from here the surface slopes abruptly toward the anterior margin, and 

 less abruptly towards the lateral margins; above the maximum convexity the surface 

 slopes uniformly to the hinge line. Surface marked by several large concentric wrinkles, 

 which gradually decrease in size toward the beak, the last two or three being quite indis- 

 tinct. Beak rounded and slightly incurved over the hinge line. A cast of the interior 

 shows the strongly marked, fan-shaped muscular imprints, divided longitudinally by 

 a median depression. 



