CAMBRIAN BRACHIOPODA — WALCOTT lOj 



Dorsal valve moderately convex except on the median fold, which 

 is rounded but not unusually prominent ; area unknown. 



Surface marked by a few concentric lines of growth. The largest 

 dorsal valve has a length of 8 mm. ; width, 1 1 mm. A ventral valve 

 9 mm. in length has a width of 14 mm. 



Casts of the interior of the valves indicate that there was a low 

 spondylium formed by a short ridge rising a little distance from the 

 center on each side ; this separates an area beneath the umbo not 

 unlike that of the ventral valve of Billingsella. There is no trace in 

 either valve of a median septum. The spondylium or chamber ap- 

 pears to have been attached to the bottom of the valves or to have 

 had the shell as its bottom ; if this view is correct, a true spondylium 

 had not been developed in this species. 



Observations. — In form this species is usually most nearly re- 

 lated to Syntrophia calcifera (Billings) [i86ia, p. 318]. It differs 

 in having a less clearly defined beak and less prominent fold on the 

 dorsal, valve. There are many points in common between Syn- 

 trophia Cambria and S. nundina (Walcott) [1905a, p. 292], but they 

 differ in the shorter beak and sharper median fold of the latter. 

 Syntrophia canibria occurs in the Wasatch range about 3,300 feet 

 below the base of the Ordovician, while S. calif era and 5. nundina 

 occur in the lower Ordovician. It is the oldest species of the genus 

 and is of interest also on account of being closely related in form to 

 the Ordovician species mentioned. 



Formation and Locality. — Middle Cambrian: (i) About i.ioo 

 feet (335.3 m.) above the top of the Lower Cambrian and 3,300 feet 

 (1,005.8 m.) below the Upper Cambrian, in the arenaceous lime- 

 stones of the Ute formation. Blacksmith Fork Section, about 8 miles 

 (12.87 km.) above the mouth of Blacksmith Fork Canyon and 15 

 miles (24.14 km.) east of Hyrum; and (2) same horizon as (i) and 

 about 10 fiiilcs south of that locality, just south of the south fork of 

 East Fork, east of Cache Valley; both in Cache County, Utah. (3) 

 About 100 feet (30.5 m.) above the Cambrian quartzites, in shales 

 of Tintic Range Section, near summit of ridge between Mammoth 

 and Eureka, Juab County, Utah. 



SYNTROPHIA CAMPBELLI, new species 



Plate to, Figures 9, ga-c 



General form rotund, unequally biconvex ; hinge line short. Ven- 

 tral valve moderately convex, exclusive of the prolonged frontal 

 margin ; it is depressed toward the front in adult shells by a broad 

 median sinus that disappears on the umbo ; area short and divided 



