232 THE DEVONIAN OF MISSOURI. 



Brachial valve slopes gently from the hinge to the front, near which it becomes 

 abruptly deflected causing a deep concavity. Concave area marked by concentric 

 wrinkles which are less pronounced than those on the opposite valve. Beak small and 

 inconspicuous. The interior casts show the strongly-marked, longitudinal muscular 

 impressions. 



Surface of both valves marked by fine, radiating costae, there being 2 or 3 present 

 in the space of 1 mm. 



Remarks — This characteristic Oriskany species occurs abundantly in the Little 

 Saline beds, and is only represented by the separate valves in the collection studied. 

 It differs from Leptaena rhomboidalis Hall, in the greater ventricosity of the pedicle 

 valve, in its larger size, and in the more strongly marked muscular imprints. The same 

 species occurs in the Oriskany sandstone of New York, and in the Oriskany beds of the 

 Gaspe region, Canada. 



Horizpn — Lower and upper beds. 



Figured specimens No. 27478 Walker museum. 



Genus Stropheodonta Hall 



Stropheodonta missouriensis sp. nov. 



Plate 61, figures 21-22. 



Description — Shell large, semi-circular in outline, width commonly greater than the 

 length, the greatest width anterior to the middle of the shell. The dimensions of two 

 brachial valves, the holotype and paratype, are: Length 38 mm., width 45 mm., and 

 length 34 mm., width 40 mm. 



Brachial valve gently concave to about 8 mm. from the anterior and lateral margins, 

 where it becomes abruptly deflected upwards. This abrupt deflection is distinctly 

 marked on the internal casts of the valves. Hinge line straight, finely crenulated, 

 shorter than the greatest width of the shell. Cardinal extremities rounded. An im- 

 pression of the interior shows part of the cardinal process, and the elongate septum ex- 

 tending more than half way to the anterior margin. Surface marked by fine, closely 

 arranged, radiating striae. 



Pedicle valve unknown. 



Remarks — There are present in the collection studied only the interior and exterior 

 impressions of the brachial valve. The form somewhat resembles Strophoedonta linck- 

 laeni Hall, but is proportionately smaller, has a more pronounced semi-circular outline, 

 more extended cardinal extremities, and with the hinge line shorter than the greatest 

 width of the shell, and lacks the curvature of the lateral margins just below the cardinal 

 angles. 



Horizon — Lower beds. 



Holotype and Paratype No. 27475 Walker Museum. 



Stropheodonta cf. demissa (Conrad) 

 Plate 61, figure 18. 



1842. Strophomena demissa Conrad, Jour. Acad. Nat. Sci., Phila., vol. 8, pi. 258, 



pi. 14, fig. 14. 

 1867. Strophodonta demissa Hall, Nat. Hist. N. Y. Pal., vol. 4, pp. 81, 101, pi. 11, figs. 



14-17; pi. 12, figs. 1-5. 

 1913. Stropheodonta demissa Schuchert, Geol. Surv., Md. Low. Dev., p. 313, pi. 57, 



fig. U. 

 Description — The only specimen referable to this species, a pedicle valve, is not 

 entirely preserved and the identification is somewhat uncertain. Shell of medium size, 

 sub-circular in outline, regularly and strongly concave. The dimensions are: Length 



