SUDCARBONIFEROUS PERIOD. 03 



This species is remarkable for its great size, and, although the speci- 

 mens of the collection are imperfect, I have hardly a doubt of their specific 

 identity with 5*. ohmaxima McChesney. 



Position and locality. — Subcarboniferous stra+a ; Mountain Spring, old 

 Mormon road, Nevada, and also at a locality below Ophir City, Utah. 



Family TEHEBUATULID^. 



Genus TEREBRATULA Lliwliyd, 1G98. 



Sur.GC.NUS DIELASMA King, 18.59. 

 Terebratula (DielaEma) Burlingtonensis White. 

 Tcrebrattda Burlingtonensis White, 18C0, Jour. Bost. Soc. Nat. Hist., 228. 



Shell of moderate size, subovate in outline, niore or less gibbous, 

 broadest a little forward of the middle. 



Ventral valve regularly convex ; beak prominent, projecting considera- 

 bly behind that of the dorsal valve, moderately incurved ; a faintly-defined 

 ridge at each side of the beak follows its curvature from the foramen for- 

 w^ard, and disappears near the middle of the shell ; dental plates moderately 

 strong, their front edges sharp and perpendicular with the teeth, placed near 

 the sides of the beak, and diverging a little as the beak increases in size ; 

 mesial sinus absent or obsolete. 



Dorsal valve depressed-convex, greatest convexity near the beak, 

 which is not prominent ; mesial fold absent. Surface smooth or marked by 

 indistinct lines of gx'owth ; shell-sti'uctnre finely punctate. 



Average length, about twenty-two millimeters. 



The type-specimens of this species were obtained from the Subcarbon- 

 iferous rocks at Burlington, Iowa, and those of the collections agree with 

 them in all essential respects. The reference to the subgenus Dielasma of 

 this species is made in consequence of the presence of dental plates, the 

 other characteristics of the subgenus not having been observed. It difi^ers 

 from T. hovideus especially in wanting the longitudinally arcuate form, so 

 constant in that species. 



Position and locality. — Strata of the Subcarboniferous period ; Mountain 

 Spring, old Monnon road, Nevada. 



