SPIRIFERINA 297 



length of brachial valve 12.8 mm., width along hinge-line 22 mm., thick- 

 ness 13.3 mm., height of cardinal area 5.8 mm., width of sinus in front 

 6 mm. 



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

 the surface curving steeply from the umbo to the anterior margin and 

 more gently to the cardinal extremities; mesial sinus angular or sub- 

 angular, sharply defined, originating at the beak, of moderate depth and 

 width ; beak small, a little incurved ; cardinal area large and high, nearly 

 flat below and lying in nearly a right angle to the plane of the valve, 

 concave above with an increasing curvature to the beak, the lateral 

 margins usually sharply defined ; the delthyrium large, much higher than 

 wide; each lateral slope marked by about five, simple, angular or sub- 

 angular plications which originate along the cardinal margin. Internally 

 a strong median septum reaches anteriorly from the beak for about one- 

 third the length of the valve, the dental plates diverge anteriorly from 

 the beak and extend about one-half as far as the median septum ; muscular 

 scars obscure. 



Brachial valve less convex than the pedicle, highest at or near the front 

 of the mesial fold, the surface sloping from the front margin of the fold 

 to the beak in an increasingly convex curve, becoming a little compressed 

 towards the cardinal extremities; mesial fold angular, sharply defined, 

 much elevated in front; cardinal area very narrow, lying in nearly a 

 right angle to that of the opposite valve ; the beak small, incurved ; each 

 lateral slope marked by angular plications similar to those of the opposite 

 valve and alternate with them. 



Surface of both valves^ marked by numerous, concentric lines of growth, 

 irregular in strength and crowded at intervals towards the front to form: 

 stronger growth lines. Shell structure minutely punctate. 



Remarks. This is the more common species of Spiriferina in the fauna 

 of the Salem limestone,' and has sometimes been identified as 8. spinosa. 

 It differs from that species in its much more elevated cardinal area, in 

 its more angular plications, more elevated mesial fold in front, and in the 

 very different style of surface markings. It is very different from the 

 diminutive S. norwoodana of the same fauna, and cannot be considered as 

 a larger form of the same species. 



Horizon. Salem limestone. 



SPIRIFERINA TRANSVERSA (McChesney) 

 Plate XXXV, Figs. 41-49 



1860. Spirifer transverse McChesney, Desc, New Pal. Foss., p. 42. 

 1865. Spirifer transversa McChesney, 111. New Spec. Foss., pi. 6, figs. 3a-c. 

 1868. Spirifer transversa McChesney, Trans. Chicago Acad. Sci., vol. 1, 



p. 34, pi. 6, figs. 3&-c. 

 1874. Spiriferina transversa Derby, Bull. Cornell Univ. (Science), vol. 1, 



No. 2, p. 21, pi. 2, figs. 4, 6, 13 ; pi. 3, figs. 12, 14, 17 ; pi. 5, fig. 4. 



