430 MISSISSIPPIAN BRACHIOPODA 



1891. Spirifer pseudolineatus? Herrick, Bull. Geol. Soc. Am., vol. 2, p. 45, 



pi. 1, fig. 18. 

 1894. Spirifer pseudolineatus Hall and Clarke, Int. to Study of Braeh., 



pt.2, pi. 25, fig. 15. 



1894. Spirifera pseudolineata Keyes, Mo. Geol. Surv., vol. 5, p. 82. 



1895. Spirifer pseudolineatus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



pi. 36, figs. 28-30. 



Description. Shell above medium size, transversely subelliptical in 

 outline with the lateral margins symmetrically rounded, length of the 

 hinge-line about two-thirds the width of the shell, the cardinal extremities 

 rounded. The dimensions of two nearly complete specimens are: length 

 of pedicle valve 32.6 mm. and 29.3 mm., length of brachial valve 28.2 mm. 

 and 24.7 mm., maximum width 38.5 mm. and 33.3 mm., length of hinge- 

 line 26 mm. and 22 mm., thickness 23 mm. and 21.4 man., height of car- 

 dinal area 6.5 mm. and 6 mm. 



Pedicle valve strongly convex, the greatest convexity posterior to the 

 middle, the surface curving abruptly from the umbonal region to the 

 cardinal margin, much less abruptly to the lateral margins and still more 

 gently to the anterior margin; mesial sinus ill-defined, usually shallow 

 and of moderate width, obsolete at the beak but originating in the 

 umbonal region ; beak rather small, pointed, incurved, projecting beyond 

 that of the opposite valve; cardinal area of moderate height, concave, 

 becoming more curved towards the beak, its lateral margins ill-defined, 

 the surface curving into that of the lateral slopes of the valve with only 

 slight differentiation, the surface vertically striate ; delthyrium broadly 

 triangular, open. Internally the hinge-teeth are supported by a pair 

 of strong dental lamella? which extend about one-fourth the length of 

 the valve from the beak towards the anterior margin, diverging at an 

 angle between 30 and 40 degrees; between the dental lamellae is a long 

 median septum which reaches to the middle of the valve or farther, being 

 from two to three times the length of the dental lamella?; the muscular 

 scars are longitudinally subrhomboidal or angularly subovate in outline, 

 with their surface usually nearly flush with the floor of the valve, their 

 anterior limit is marked by a slightly raised ridge passing from the 

 posterior termination of the dental lamella? to the posterior extremity 

 of the median septum, the anterior portion of the ridge being gently 

 convex and the posterior half usually nearly straight ; the entire inner 

 surface of the valve, even that of the cardinal area and the greater part 

 of the muscular scar, is covered by fine radiating costa?, from 2 to 5 

 of which occupy the space of 1 mm. 



Brachial valve less convex than the pedicle, the greatest convexity 

 near or posterior to the middle, the surface curving abruptly from the 

 umbonal region to the cardinal margin and more gently to the lateral and 

 anterior margins, sometimes very slightly compressed towards the car- 



