234 THE DEVONIAN OF MISSOURI. 



or in some examples the length and width equal. The pedicle valve of an average 

 sized individual measures 45 mm. from beak to anterior margin, and 50 mm. across the 

 greatest width. The largest individual observed measures 75 mm. in length and 80 

 mm. in width. 



Pedicle valve regularly convex, without median sinus. Beak flattened, incon- 

 spicuous, scarcely incurved over the hinge line. In the older individuals the surface of 

 the shell in the pallial region is folded to form broad wrinkles. Large longitudinal muscle 

 impressions are conspicuous in the casts of the interior, the divisions being marked off by 

 distinct grooves, the whole scar fan-shape in outline. 



Brachial valve from flat to slightly concave. The surface of the vascular area is 

 characterized by numerous pustulose elevations, irregularly arranged, and which be- 

 come faint towards the margins. The impressions of the two adductor muscle scars are 

 sub-reniform in outline, and are separated by a low, rounded ridge. 



The entire surface of both valves is marked by fine, radiating slightly flattened 

 costae, with coarser concentric lines of growth crossing them. The costae vary con- 

 siderably in size, and increase by bifucation and intercalation, the additions being most 

 conspicuous a little below the beak. In exfoliated portions of the shell a distinct pitted 

 structure is apparent, the pits arranged in longitudinal rows parallel to the striae. 



Remarks — This species occurs abundantly in the Little Saline limestone, and is repre- 

 sented by separate valves only, pedicle valves and their casts being most frequent. 

 The specimens agree closely with those from the Oriskany of New York and attain a 

 similar size. 



Horizon — Lower and upper beds. 



Figured sptcimens No. 27474 Walker Museum. . 



Leptoslrophia magniventra Hall 

 Plate 62, figures 4-5. 



1857. Strophodonta magniventra Hall, Tenth Ann. Rept. N. Y. State Cab. Nat. Hist. 



p. 54. 

 1859. Strophodonta magniventra Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 411, pi. 92, 



figs. 2a-2c, 3; pi. 95, fig. 9, 1861. 

 1859. ? Strophodonta lincklaeni Hall, Nat. Hist. N. Y. Pal., vol. 3, pi. 93, fig. 2a (not 



figs. 3a, 3b^5. lincklaeni). 

 1859. Strophodonta vascularia Hall, Nat. Hist. N. Y. Pal., vol. 3, pi. 93, figs. 2b, 2c 



(not pi. 92, fig. 4; pi. 95, fig. 10=5. magnifica) 1861. 

 1861. Strophomena magniventra Billings, Can. Jour. Sci. Arts, vol. 6, p. 349. 

 1863. Strophomena magniventra Billings, Geol. Can., p. 961, fig. 469. 

 1874. Strophomena magniventra Billings, Pal. Fossils, vol. 2, p. 22, figs. 10-12, pi. 2, 



figs. 2-2a. 

 1892. Stropheodonta {Leptoslrophia) magniventra Hall and Clarke, Nat. Hist. N. Y. 



Pal., vol. 8, pt. 1, p. 288, pi. 13, figs. 25-26. 

 1900. Stropheodonta licklaeni Clarke, Mem. N. Y. State Mus., vol. 3, No. 3, p. 52, 



pi. 7, fig. 37. 

 1913. Stropheodonta (Leptoslrophia) magniventra Schuchert, Geol. Surv., Md. Low. 



Dev., p. 319, pi. 58, figs. 6-8. 

 Description — Shell elongate oval to semi-circular in outline, relative length and 

 width variable. The dimensions of the only complete mature pedicle valve observed 

 are: Length 41 mm., width 49 mm. The pedicle valve of a larger and probably older 

 individual measures 50 mm. in length and approximately 60 mm. in width. 



Pedicle valve of medium convexity, the surface sloping gradually and uniformly 

 to the lateral and anterior margins with no fold or sinus. Hinge line slightly less than 

 the greatest width of the shell, the greatest width a little posterior to the middle of the 



