558 GEOLOGY OP THE YELLOWSTONE NATIONAL PAKK. 



The ventral valve is strongly arched in an anterolateral direction, 

 somewhat flattened transversely, with a broad, shallow sinus which can be 

 traced quite to the beak, losing' distinctness as it grows broader. Beak 

 high, strongly incurved. Area triangular and not well defined. Foramen 

 large and high. Surface marked by about twenty-six fine, low plications, 

 about six of which lie in the sinus, and with about ten on either wing. 

 The shell is superficially marked by innumerable fine pits, much resembling 

 the punctation in the genus Spiriferina, but this character is restricted to a 

 thin outer layer, beneath which the shell substance is fibrous and impunc- 

 tate. This appearance is probably secondary, resulting from an originally 

 spinose exterior, which, with the general character of the species, elongate 

 shape and obsolescent plications, distinguishes it from any representative 

 of the genus Spiriferina, and seems to denote an alliance with Reticularia. 



As regards its specific position, a comparison with typical Spirifera 

 subrohmdata Hall, from the yellow sandstone of Burlington, Iowa, leads me 

 to believe that it is identical with that species. 



B. subrotundata is in many ways comparable to JR. peculiaris, but the 

 character of the plications affords an easy basis for discrimination. R. sub- 

 rotundata has finer and more numerous plications, of which six or more are 

 in the fold and sinus, while in B. peculiar-is the fold and sinus are undivided. 



The same form occurs in the lower Burlington of Pike County, Mis- 

 souri, and seems to have been usually identified as B. peculiar is. 



Formation and locality: Madison limestone, Little Belt Mountains, 

 east side of Belt Creek, 5 miles above Monarch, Montana; W. H. Weed. 

 Lower Burlington chert, Pike County, Missouri. 



SYRINGOTHYRIS A. Winchell, 1863. 



Syringothyris carteri Hall. 



PL LXXI, figs. l«, l&, ic. 



ISpirifer carteri Hall, 1857: Tenth Ann. Rept. New York State Cab. Nat. Hist., p. 170. 

 (partim) Meek, 1S75: Pal. Ohio, Yol. II. p. 2S5 (not his figures = #. texta Hall). 



Spirifer (Cyrtiaf) hannibalensis Swallow, 1S60: Trans. St. Louis Acad. Sci., Yol. I, 

 p. 647. 



Syringothyris typa Winchell, 1S63: Proc. Acad. Nat. Sci. Philadelphia, p. 7. Winchell, 

 1870: Proc. Am. Phil. Soc, Yol. XI, p. 252. Hall and Clarke, 1893: Pal. New 

 York, Vol. VIII. Pt. II, p. 48, fig. 40. Hall and Clarke, 1895: Pal. New York, 

 Yol. VIII, Pt. 11, PI. XXVI, figs. 6, 7, 10; PI. XXVII, figs. 1-3. 



