ACKOTRETID^. 699 



This form owes its varietal name to the fact that it occurs higher in the section than the 

 species, and is probably descendant from it. 



Formation and locality. — Middle Cambrian: (30n) About 3,750 feet (1,143 m.) above the Lower Cambrian and 

 650 feet (198 m.) below the Upper Cambrian in shaly limestones forming Ic of the Weeks limestone [Walcott, 1908f, 

 p. 175], on the north side of Weeks Canyon, about 4 miles (6.4 km.) south of Marjum Pass, House Range [Walcott, 1908t, 

 PI. XIII], Millard County, Utah. 



ACEOTEETA OPHIEENSIS EUGOSA Walcott. 



Plate LXXIV, figures 2, 2a-e. 



Acrotreta ophirensis rugosus Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 592. (Characterized as below as a new 

 variety.) 



This form is associated with Acrotreta ophirensis Walcott in considerable numbers. It is 

 characterized by strong, rugose growth lines and thicker shell. 



Formation and locality. — Middle Cambrian : (3e) Thin-bedded limestone, less than 400 feet (121.9 m.) above 

 the quartzitic sandstones of the Cambrian, at Ophn, Oquirrh Range, Tooele County, Utah. 



LX 



AcEOTEETA OVALIS Walcott. 

 Plate LXVI, figures 2, 2a-b. 

 Acrotreta ovalis Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 592. (Characterized as below as a new species.) 



In material received from the Geological Survey of Canada in answer to a request for the 

 specimens representing Acrotreta gemma Billings, there was one ventral valve embedded in a 

 smooth, dove-colored limestone from Point Levis. This specimen differs materially from A. 

 gemma in the oval outline of the rim of the shell, less elevated apex, and less well-defined false 

 area. It is more of the type of A. schmalenseei Walcott, and of A. Tnicroscopica (Shumard) of 

 the interior continental species than any of the Atlantic Province forms. 



Formation and locality. — Lower Ordovician: (319 [Geol. Sui-vey, Canada]) Limestone No. 1 of Billings's Point 

 Xevis Section, Point Levis, Province of Quebec, Canada. 



AcEOTEETA PACIFICA Walcott. 

 ^ Plate LXIX, figures 6, 6a-e. 



Acrotreta pacifica Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 301. (Described below as a new species.) 



Ventral valve a high cone, with the apex a little in advance of the posterior margin; base 

 •circular, with the exception of a slight flattening on the posterior side; apex acute and pointing 

 upward; false area only a slight flattening of the shell from the apex to the margin. The 

 largest ventral valve has a diameter and height of about 1.5 mm. Surface marked by fine 

 concentric striae that continue without noticeable deflection across the false area. 



Observations. — Only two specimens of the ventral valve of this species occur in the collec- 

 tion. One of these has a slightly transverse, broadly oval base, and a more definite false area. 

 ■The species is closely related to Acrotreta idahoensis alta Walcott except that the ventral valve 

 is not quite as elevated. 



Formation and locality. — Middle Cambrian: (CI and C2) Lower shale member of the Kiulung group [Black- 

 -welde'r, 1907a, pp. 87 and 40 (part of the 3d list of fossils) and fig. 10 (beds 4 and 5), p. 38], 2 miles (3.2 km.) south of 

 Yenchuang; (C12) gray limestone near the top of the middle limestone member of the Kiulung group [Blackwelder, 

 1907a, pp. 37 and 41 (part of the first list of fossils) and fig. 10 (bed 7), p. 38], 3.25 miles (5.2 km.) southwest of Yen- 

 chuang; (C5) lower limestone member of the Kiulung group [Blackivelder , 1907a, pp. 37 and 39 (first list of fossils), and 

 Jig. 8a (bed 30), p. S9], 3.2 miles (5.1 km.) southwest of Yenchuang; and (C4) limestone nodules at the base of the lower 

 shale member of the Kiulung group [Blaclcwelder, 1907a, pp. 37 and 40 (2d list of fossils), and fig. 10 (bed 4), p. 38], 

 3 miles (4.8 km.) southwest of Yenchuang; all in the Sintai district. Shantung, China. 



AcEOTEETA PAEVULA (Wallerius). 



^' Plate LXXVII, figures 4, 4a. 



■Obolella parvula Wallerius, 1895, Undersokningar ofver Zonen med Agnostus Ixvigatus i Vestergotland, pp. 65-66, 



figs. 9a-d. (Described in Latin, and discussed in Swedish.) 

 .A.crotreta parvula (Wallerius), Walcott, 1902, Proc. U. S. Nat. Mus., vol. 25, p. 592. (Described as on p. 700.) 



