120 PROCEEDINGS OP THE ACADEMY OP 



long as the greatest width of the shell, forming a rounded right angle 

 with the short lateral margins ; area triangular, three and a half times as 

 long as high, arched in the quadrant of a cylinder, striated in both directions, 

 pierced by a foramen reaching to the very apex of the beak, nearly twice as 

 high as broad, rounded at its upper angle. Mesial sinus deep, broad, regular, 

 beginning at the apex of the beak, the bounding ribs forming with each other 

 an angle of about 22 ; on each side of the sinus five large plications, of which 

 only the first three reach the beak, the others terminating at the area ; these 

 are crossed by sharp, neat, imbricating lamellae of -growth, of which, in the 

 middle of the valve, about four occur in one-tenth of an inch. Dental plates 

 short, columnar ; a median internal septum reaching from a point a little 

 posterior to the teeth, as far as the middle of the valve, thick at the bottom, 

 thinned to an edge above. Internal surface of valve marked with numerous 

 indented punctations. Dorsal valve unknown. 



Length, -48 (71) ; breadth, -68(100); length of hinge line, -52(79); 

 height of area, -15 (22) ; convexity of ventral valve, -22 (33). 



From the Lithographic limestone, Clarksville, Missouri. " White Collec- 

 tion " of the University of Michigan. 



This species bears perhaps too close a resemblance to S. solidirostris, White. 

 The single valve, however, on which the species is founded, is more convex, 

 with more rounded ribs, less regular lamella?, a higher area and more incur- 

 ved beak. This is the specimen referred to by White, (Boston Proc. ix. 25,) 

 and doubtfully identified with S. subtexta, White a Burlington limestone 

 species. 



Spiriferina binacuta, n. sp. Shell of moderate size, transverse, with nu- 

 merous rounded ribs and attenuate hinge extremities. Dorsal valve some- 

 what ventricose in the middle, regularly arched from anterior margin to the 

 beak, becoming depressed toward the lateral extremities. Hinge line elon- 

 gate, thickened at the margin, abruptly acuminate. Area narrow and long. 

 Mesial fold little elevated above the general surface, divided by a furrow into 

 two ribs, which, in old specimens, are again divided ; ten or eleven rounded 

 ribs on each side of the mesiaf fold, of which the last two or three are subob- 

 solete. External surface finely and regularly lamellose. Substance of shell 

 thin and apparently possessing a rather coarsely punctate structure. 



Length of hinge line, -78 ; length from beak to base, -30. 



This species is readily distinguished by its auricular acuminations and pli- 

 cate mesial fold. 



From the base of the Burlington limestone. "White Collection" of the 

 University of Michigan. 



Spiriferina solidirostris, White. From near Hamburg, Illinois. "White 

 Collection." The ribs are more rounded than in the specimens from the Bur- 

 lington sandstone. The same species occurs associated with S. binacuta in 

 the base of the Burlington limestone. 



RHYNCHONELLA, Fischer de Waldheim. 



Rhtnchonella ? tetrapttx, n. sp. Shell minute, subcircular in outline, 

 with few and deep plications. Ventral valve moderately convex, highest in the 

 middle, with a straight projecting beak, which is circularly perforate at apex, 

 with a triangular opening below to the hinge. Along the middle of this valve 

 is a very deep and very narrow sinus reaching nearly to the beak, and bound- 

 ed by a very prominent rib on each side, beyond which is another smaller rib, 

 making four in all. Dorsal valve almost strictly circular, with the same con- 

 vexity as the ventral, highest also in the middle, with the inconspicuous beak 

 closely appressed, and the middle raised into a strong plication or rib corres- 

 ponding to the sinus or furrow of the ventral valve ; on each side of this rib 



[July, 



