OBOLELLID^. 609 



Type. — ScMsopTiolis rugosa Waagen. 



Ohservations. — The generic relations of this shell, as far as can now be determined, are 

 with Acroihele. With our present information it differs only in its more marked false del- 

 tidium. 



The interior of a dorsal valve from the same bed of sandstone is tentatively referred to 

 this species (PI. I, fig. 4c). The area of the valve is narrow and not clearly defined; it appears 

 to be merged into a small projecting platform that extends in front into a strong median ridge; 

 at each side of the ridge the platform-like area overhangs a little so as to form a slight hollow 

 beneath; the median ridge extends nearly to the front margin of the shell, very much as in 

 the dorsal valve of Acrotreta sagittalis (Salter) (PL LXXI, fig. 3g). 



My interpretation of this shell differs somewhat from that of Waagen [1885, p. 752]. 

 This arises from his thinking that the false deltidium was an open fissure. On cleaning away 

 the dirt I find that there is a depressed triangular space and that the lines and stria3 of growth 

 cross the false area and the false deltidium; also that the foraminal opening is a simple cir- 

 cular aperture as in Acrothele. 



ScHizoPHOLis ETJGOSA Waagen. 

 Plate I, figure 4c; Plate LXXXI, figures 1, la-c. 



Sehizopholis rugosa Waagen, 1885, Mem. Geol. Survey India, Paleontologia Indica, 13th ser., Salt Range Fossils, vol. 



1, pt. 1, pp. 753-754, PI. LXXXVI, figs. 2-A. (Described and discussed as a new species. The specimens rep- 



resented by figs. 3 and 4 are redrawn in this monograph, PI. LXXXI, figs. Ic and 1, la-b, respectively.) 

 Sehizopholis rugosa Waagen, 1891, idem, vol. 4, pt. 2, PI. II, figs. 12-14. (No text reference. With the exception of 



fig. 4c, which is not copied in 1891, figs. 13, 14, and 12 are copied from figs. 2^, .respectively, of the preceding 



reference.) 

 Sehizopholis rugosa Waagen, Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York for 1891, p. 248, 



figs. 259 and 260. (No text reference. Figs. 259 and 260 are copied from Waagen, 1885, PL LXXXVI, figs. 



4d and 4b, respectively.) 

 Sehizopholis rugosa Waagen, Hall and Clarke, 1892, Forty-fifth Ann. Rept. New York State Museum for 1891, p. 564, 



figs. 259 and 260. (Copy of preceding reference.) 

 Sehizopholis rugosa Waagen, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 95, figs. 50 



and 51. (Mentioned in discussion of genus Sehizopholis. Figs. 50 and 51 are copied from Waagen, 1885, 



PL LXXXVI, figs. 4d and 4b, respectively.) 



General form ovate. Ventral valve slightly convex, greatest elevation at the apex, which 

 is nearly above the posterior margin; apex minute and perforated by a circular opening. The 

 posterior side of the shell beneath the apex is slightly flattened so as to form a false area, divided 

 midway by a false deltidium formed by the arching of the lines and strise of growth; an angle 

 is formed at the point where the fines and strise arch upward, which gives form to the slight 

 depression, or the false deltidium. Dorsal valve nearly flat, except near the umbo, which is 

 slightly elevated, apex marginal, minute. 



Surface marked by numerous concentric lines and strise of growth, and irregular, inter- 

 rupted, slightly elevated, radiating ridges that vary in size and direction on different shells. 

 The shell is thin on the edges, becoming thicker toward the umbonal portions by the addition 

 of thin layers or lamellse. The type specimen of the ventral valve has a length and width of 

 6 mm. 



Observations. — This species is allied to Botsfordia cxlata (Hall). It differs in surface charac- 

 ters, general outline, and the presence of a false deltidium and area. 



Formation and locality. — Middle Cambrian: (357c [Waagen, 1885, p. 754]) Lower portion of the "Neoholus 

 beds" of the Khussak group, in purplish-colored, fine-grained, micaceous sandstone, near the fresh-water springs in a 

 gorge above the salt mines at Kiura (Khewra), Salt Range, India. 



Genus QUEBECIA Walcott." 



Quebecia Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 320. (Mentioned as on p. 610 as a new genus.) 



Quebeda Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PL XI, and pp. 142 and 145. (Classification of genus.) 



a The sjTionymy for ttiLs genus does not give a complete record of the various genera under which the species now included in Quebecia were 

 formerly placed; it gives only those references in which the genus is discussed or described. To complete the record the following generic 

 references are 1 isted : 



Obolella Billings [1872a, p. 219; 1372c, p. 357]. OboleUa Walcott [1886b, p. 118; lS91a, p. 611). 



62667°— VOL 51, pt 1—12 39 



