SYNTEOPHIID^. 80S> 



p. 191]; and (54o) about 1,100 feet (335.3 m.) above the Middle Cambrian and 120 feet (36.6 m.) below the top of the' 

 Upper Cambrian in the central part of the limestone forming 1 of the St. Charles formation [Walcott, 1908f, p. 192];; 

 both in Blacksmith Fork Canyon about 10 miles (16.1 km.) east of Hyrum, Cache County, Utah. 



A specimen (PI. CII, fig. 4d) that is somewhat doubtfully referred to this species occurs 

 at the following locality: 



Upper Cambrian: (329a) Limestone on Ute Peak, in the Wasatch Mountains east of Cache Valley, Cache County, 

 Utah. 



Syntrophia orthia Walcott. 



Plate CIV, figures 4, 4a-b. 



Syntrophia orthia Walcott, 1905, Proc. U.S. Nat. Mus., vol. 29, pp. 11-12. (Described and discussed as a new species.) 



General form irregularly oval, with the ventral view obtusely angular toward the apex; 

 rounded, biconvex, with a deep mesial sinus on the ventral valve and a strong median fold on 

 the anterior half of the dorsal valve. Surface smooth, with the exception of a few concentric 

 striag and lines of growth. The ventral valve has a strong median sinus that occupies about 

 one-third of the width of the valve at the anterior margin and projects forward to fit into the 

 sinus in the front of the margin of the dorsal valve; the sides of the median sinus are elevated, 

 and with the downward-sloping lateral slopes form a strong, rounded ridge on each side of the 

 sinus; none of the specimens in the collection show the area, but from the profile of the valve 

 it must have been of moderate height, with a rather sharp apex curving over it. 



Dorsal valve with a minute apex, from which a narrow, slightly developed median fold 

 extends to about the posterior fourth of the shell, where it becomes elevated, and, widening, 

 extends forward to the front margin ; the remaining portions of the surface are uniformly convex, 

 sloping away from the median fold to the margins of the valve. 



Nothing is known of the interior of either valve. 



Observations. — In general form this species resembles Syntrophia primordialis (Whitfield) 

 of the "St. Croix sandstone" of Wisconsin. It differs in its more rounded, irregularly oval form 

 and the very large median sinus of the ventral valve. 



Formation and LOCALiTY.^Upper Cambrian: (C54) Lower part of the Chaumitien limestone [Blackwelder, 

 1907a, p. 42 (part of last list of fossils)], 0.66 mile (1.1 km.) west of Tsinan; (C56) same horizon as Locality CS4 at 

 Pagoda Hill [Bladcwelder, 1907a, p. 4^ (part of last list of fossils}], 1 mile [1.6 km.) west of Tsinan; and (C64) upper 

 limestone member of the Kiulung group [Blackwelder, 1907a, pp. 37 and 42 (first list of fossils), and fig. 10 (bed 20), 

 p. 38], 2.7 miles (4.3 km.) southwest of Yenchuang, Sintai district; all in Shantung, China. 



Syntrophia primordialis (Whitfield). 



Plate CII, figures 2, 2a-e. 



Triplesia primordialis Whitfield, 1878, Ann. Kept. Wisconsin Geol. Survey for 1877, p. 51. (Described.) 



Triplesia primordialis Whitfield, 1882, Geol. Wisconsin, vol. 4, pt. 3, p. 172, PI. X, figs. 1 and 2. (Described and 



discussed, the first paragraph being copied below.) 

 Triplecia? primordialis Whitfield, Hall and Clarke, 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 270, 



footnote. (Questions generic reference.) 

 Syntrophia primordialis (WTiitfield), Hall and Clarke, 1893, idem, pt. 2, p. 218. (Changes generic reference.) 

 .Syntrophia primordialis (Wbitfield), Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 292. (Whitfield's description, 



1882, p. 172, copied and species discussed as below.) 



The description by Whitfield [1882, p. 172] follows: 



Shell small, measuring less than half an inch in width; transversely oval in outline, and quite ventricose in profile; 

 hinge line straight and about half as long as the width of the shell below; area narrow. Ventral valve with a strongly 

 depressed, rather narrow and rounded mesial sinus. Dorsal valve with a narrow, sharply elevated fold not extending 

 quite to the beak; sides of the valve rounded. Surface smooth in the casts, but presenting the appearance of having 

 been externally striate. Processes in the interior of the dorsal valve apparently forming a small spoon-shaped pit at 

 the beak. 



Observations. — Casts of the interior show the form of the spondylium and supporting 

 median septum in the ventral valve; also, a small short spondylium in the ventral valve, which 

 appears to be attached to the bottom of the valve without a median septum. 



