I06 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



A large ventral valve has a length of 8 mm. ; width, 9 mm. Sub- 

 stance of shell unknown. 



Observations. — This species was at first compared with Nisusia 

 (Jamesella) nautes (Walcott) [1905a, p. 283], but the surface ribs 

 are more regular and less numerous. It also occurs 1,800 feet 

 (548.6 m.) higher in the stratigraphic section than the fauna of A'. 

 (/. ) nautes. 



Formation and Locality. — Middle Cambrian: (i) About 2,250 

 (685.8 m.) above the top of the Lower Cambrian and 2,150 feet 

 (655.3 m.) below the Upper Cambrian, in the gray shaly limestones 

 of the Marjum formation ; and (2) about 2,4^,0 feet {746.8 m.) above 

 the top of the Lozver Cambrian and 1,950 feet {594.4 ni.) belozv the 

 Upper Cambrian, in the thin-bedded limestones of the Marjum for- 

 mation, House Range Section; both 2.5 miles (4.02 km.) east of 

 Antelope Springs, in ridge surrounding Wheeler Amphitheater, 

 House Range, Millard County, Utah. 



EOORTHIS ZENO, new species 



Plate 10, Figure 8 



In outline the ventral valve of this species is somewhat similar to 

 that of some forms of Eoortliis remnicha zvinfieldensis (Walcott) 

 [1905a, p. 270], but it differs in having finer radiating ribs and in 

 its smaller size. It is also much smaller than Boorthis nezvberryi, 

 and it occurs 4,400 feet lower in the same stratigraphic section. I 

 do not know of any similar form with such regular, fine, sharp, radi- 

 ating ribs from the Cambrian terrane. The largest ventral valve in 

 the collection has a length of 10 mm. ; width, 18 mm. 



Formation and Locality. — Middle Cambrian: About 1,100 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- 

 stone of the Ute formation, in the 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, Cache County, Utah. 



Genus SYNTROPHIA Hall and Clarke [1892^^, p. 270] 

 SYNTROPHIA CAMBRIA, new species 



Plate 10, Figures ii and iia 



General form transversely oval, strongly convex, but not rotund. 

 Ventral valve moderately convex, with the frontal margin in adult 

 shells prolonged ; a flattened median sinus begins on the umbo and 

 widens to two-thirds the width of the shell in front ; area unknown. 



