290 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxviii. 



and very stroiiii main \ asciilar .sinuses; l)()tli spondyliuin and sinuses 

 rocall those of liiUiiKjHcJla pliattdla. Sortions of the ventral valve 

 cut across the umbo show the spondylium attached to the bottom of 

 the valve. The tiabelliform diductor and adductor muscle scars are 

 clearly- shown outside of the vascular sinuses. 



Dorsal valve with an elevated median fold that gives a strong con- 

 vexity to the valve; area low, with a strong, open delthj^rium; the 

 interior of the valve shows a shallow spondylium attached to the bot- 

 tom of the valve posteriorly, and prol)ably supported by a low median 

 septum toward the front, and well defined anterior and posterior 

 adductor muscle scars; narrow main vascular sinuses occur, and slender 

 vascular lines radiate forward from the muscle scars. 



Ohservatloux. — This species differs from all allied forms by its vari- 

 ation in outline, convexity, ribs and internal markings. Some shells 

 approach closely to those of S. texaiKi^ but each species has a majority 

 of shells that are <|uite unlike those of the other. Another point of 

 resemldance is the form of the spondylium as shown by cross sections. 

 A variety of S. te.rdna from CV)ld Creek Canyon, Texas, has some 

 shells that approach those of S. <(hri<>i'mis in the extravagant develop- 

 ment of the fold on the dorsal valve and sinus on the ventral valve, 

 but in other respects the}- diff'ei- from it. The form of the spond^dium 

 and plications or ribs, suggests the genus Pnr<ixtro'p}da Hall. 



Foi'in(di(ni and locality. — Upper Cambrian. Head of Deep Creek 

 Yellowstone National Park, Wyoming. North of East Gallatin 

 River, near Hillsdale, Dry Creek, Gallatin Valley, Montana. 



SYNTROPHIA ALATA, new species. 



This species is characterized l)y its transverse form and extended 

 cardinal angles. P^xterior surface marked by concentric striw and 

 lines of growth and interior surface by tine, radiating strite. A trans- 

 verse section of the ventral valve at the umbo shows the spondylium 

 with a strong median septum supporting it. The interior of the ven- 

 tral vahe was marked by two strong main vascular sinuses starting 

 from the sides of the spondylium. 



Foraiatlon and locality. — Upper Cambrian. Honey Creek, Burnett 

 County, Texas. 



SYNTROPHIA BARABUENSIS A. Winchell. 



OrUih hiralmeimx A. Winchell, Am. Jour. 8ci., 2(1 ser., XXXVII, 1864, p. 228. 

 Leptu'int Ixtralnicuah WiiiTFiKLi), Ann. Rep. Geol. Survey Wisconsin, 1877, p. 60. 

 Leptivna Ixvrahueims WiiiTKrRLi), (Jeology of Wisconsin, IV, 18S2, pp. 171, 195, 



pi. I, ti<is. 6, 7; pi. HI, lig. 6. 

 Sy'niroj)hiaharabue)iiih¥{\\ArAi\dCi,\RViv., Pal. New York, VIII, 1893, Pt. 2, p. 216. 



J>c.scnj)ll()ii {1)1/ Mr. Wltitfiehl). — Shell of medium size or smaller, measuring about 

 half an inch or less than half an inch along the hinge line; form semielliptical, long- 

 e.st on tJie hinge and more than half as wide again as long; extremities of the hinge 



