298, MISSISSIPPIAN BRACHIOPODA 



1883. Spirifera transversa Hall, Kep. N. Y. State Geol. for 1882, pi. (35) 

 60, figs. 19-25. 



1894. Spiriferina transversa Hall and Clarke, Int. to Study of Brach., 



pt. 2, pi. 31, figs. 1-3. 



1895. Spiriferina transversa Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, 



pi. 35, figs. 19, 20, 23-25. 



Description. Shell below medium size, broadly subtriangular in outline, 

 usually more than twice as wide as long and the thickness about equal to 

 the length, the cardinal extremities acutely pointed. The dimensions of a 

 very perfect specimen are : length of pedicle valve 10 mm., length of 

 brachial valve 9 mm., width along hinge-line 25.1 mm., thickness 9.6 mm., 

 height of cardinal area 3 mm., width of mesial sinus in front 4.2 mm. 



Pedicle valve strongly convex, most prominent in the umbonal region, 

 the surface sloping from the umbo to the cardinal extremities in a nearly 

 straight or slightly concave line and curving strongly to the anterior 

 margin; the mesial sinus originating at the beak, of moderate width and 

 depth, sharply defined, marked by a single median plication which orig- 

 inates in the umbonal region ; the beak rather small, pointed and incurved ; 

 cardinal area large, concave, with the curvature increasing towards the 

 beak, its lateral margins sharply defined, its lower, flatter portion standing 

 at nearly a right angle to the plane of the valve ; delthyrium large, nearly 

 as wide as high ; each lateral slope marked by from ten to twelve simple, 

 rounded plications which originate along the cardinal margin, those 

 bounding the mesial sinus are the largest and they grow regularly 

 smaller towards the cardinal extremities, the last ones being very faint 

 or nearly obsolete. Internally a strong median septum extends from 

 the beak to about the middle of the valve, the hinge-teeth are strengthened 

 by dental lamella? which continue to the floor of the valve and diverge 

 anteriorly, extending about one-half or a little less than one-half as far 

 as the median septum. 



Brachial valve less convex than the pedicle, the greatest convexity 

 posterior to the middle, the surface curving abruptly from the point of 

 greatest convexity to the cardinal margin and more gently to the anterior 

 margin, towards the cardinal extremities the surface is somewhat com- 

 pressed ; mesial fold sharply defined, originating at the beak, flattened on 

 top and marked by a median furrow which originates back of the middle 

 of the valve; the beak small, strongly incurved; the cardinal area very 

 narrow, making an angle of about 90 degrees to that of the opposite 

 valve; each lateral slope marked by plications similar to those of the 

 opposite valve and alternate with them. Internally, the cardinal process 

 is of moderate size and is flanked by the rather strong crural plates in 

 the outer faces of which the dental sockets are excavated ; the muscular 

 scars are weakly developed and are divided longitudinally by a faint 

 median ridge. 



