DESCRIPTION OF GENERA AND SPECIES. 63 



A ventral valve 3 mm. in width has a length of 2.75 mm. and a height of i mm. 

 A dorsal valve with a width of 2.5 mm. has a length of 2 mm. and a height of 0.5 

 mm. at the beak. 



In form the ventral valve of this species is not unlike that of Micromitra sculp- 

 tilis (Meek) [p. 61], except that it is not so elevated and its surface is quite different. 

 It is associated with M. scnlptilis and the two varieties of Micromitra (Iphidella) 

 pannula, ophirensis and maladetisis. 



Formation and Locality. Middle Cambrian: Fu-chou series: (35n and 35 r) 

 limestones and (36 d) shales near the base, just above the white quartzite [see Black- 

 welder, 19076, p. 92, for general section giving stratigraphic relations] ; collected in a 

 low bluff on the shore of Tschang-hsing-tau Island, east of Niang-niang-kung, Liau- 

 tung, Manchuria, China. 



Collected by J. P. Iddings and Li San. 



IPHIDELLA Walcott, Subgenus of MICROMITRA. 

 For discussion of the subgenus see Monogr. U. S. Geol. Survey, vol. LI, 



1912, P- 359- 



Micromitra (Iphidella) pannula maladensis (Walcott). 



Plate i, Figures 9, go. 

 Iphidella pannula maladensis WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvni, p. 306. (Description 



of variety.) 



Micromitra (Iphidella) pannula maladensis (WALCOTT), 1912, Monogr. U.S. Geol. Survey, vol. LI, p. 364, 

 plate iv, figs. 2, 2a-g. (Describes and illustrates the variety.) 



This beautiful shell has been found in Newfoundland with the Atlantic Province 

 Middle Cambrian fauna and in southern Idaho with the Rocky Mountain Province 

 fauna [Walcott, 1912, p. 364, Monogr. LI]. It differs from the variety ophirensis 

 of this species, with which it is associated (35 n) in having a more network-like 

 surface of sharp elevated ridges, and from M. (I.) pannula in having the surface 

 network formed of sharper concentric ridges modified by fine, rounded, radiating 

 ridges. These differences are shown by the illustrations on plate iv, Monogr. 

 U. S. Geol. Survey, vol. LI. 



Formation and Locality. Middle Cambrian: (35 11 and 35 r) Fu-chou series; 

 limestones near the base just above the white quartzite [see Blackwelder, 19076, 

 p. 92, for general section giving stratigraphic relations]; collected in a low bluff on 

 the shore of Tschang-hsing-tau Island, east of Niang-niang-kung, Liau-tung, Man- 

 churia, China. 



Collected by J. P. Iddings and Li San. 



Micromitra (Iphidella) pannula ophirensis (Walcott). 



Plate i, Figures 10, loa-b. 

 Iphidella pannula ophirensis WALCOTT, 1905, Proc. U.S. Nat. Mus., vol. xxvni, p.3o6. (Characterized 



as a new variety.) 



Micromitra (Iphidella) pannula ophirensis (WALCOTT), 1912, Monogr. U.S. Geol. Survey, vol. LI, p. 365, 

 plate IV, figs. 4, 4<i-/. (Describes and illustrates the variety.) 



This variety of Micromitra (Iphidella} pannula is represented by several fine 

 specimens occurring in a limestone similar in character to the limestone at Ophir 

 City, Utah, containing the American specimens [Walcott, 19126, p. 365]. In form 

 and surface characters the shells from the two widely separated localities appear 

 to be identical. 



Formation and Locality. Middle Cambrian: (35 n) Fu-chou series; limestones 

 near the base, just above the white quartzite [see Blackwelder, 19076, p. 92, for 

 general section giving stratigraphic relations] ; collected in a low bluff on the shore of 

 Tschang-hsing-tau Island, east of Niang-niang-kung, Liau-tung, Manchuria, China. 



Collected by J. P. Iddings and Li San. 



