PATERINID^. 349 



Iphidea bella Hall and Clarke (in part) [not Billings], 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, p. 98, 

 PI. IV, figs. 8 and 9 (not fig. 54, p. 98, which is refen-ed in this monograph to Micromitra (Paterina) bella). (Men- 

 tioned in the text. Figs. 8 and 9 are copied from Hall and Clarke, 1892a, PI. IV, figs. 4 and 5, respectively.) 



Iphidea labradorica Schuchbkt (in part) [not (Billings)], 1897, Bull. U. S. Geol. Survey No. 87, p. 234. (Accepts 

 Billings's reference of "Obolus labradoricus" to Iphidea, but includes reference to specimens of both Micromitra 

 [Paterina) labradorica and its variety swantonensis .) 



Iphidea labradorica swantonensis (Walcott), Schuchert, 1897, idem, p. 234. (Merely changes generic reference.) 



Iphidella labradorica swantonensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 307. (Merely changes generic 

 reference.) 



Iphidea swantonensis (Walcott), Grabau and Shimbr, 1907, North American Index Fossils, vol. 1, p. 201, figs. 234i 

 and 234j, p. 199. (Described. Figs. 234i and 234] are copied from Walcott, 1886b, PL IX, figs. 2a and 2b, 

 respectively.) 



The general form of the two valves of tliis variety is so close to that of Micromitra (Paterina) 

 labradorica (Billings) (p. 347) that it will not be necessary to repeat the description. The dif- 

 ferences existing in the variety swantonensis have been mentioned in describing the species. 

 The variety is exceedingly abundant in the Ole7ieTlus-hea.rmg limestone, 2 miles (3.2 km.) east of 

 Swanton, Vermont, in association with Kutorgina cingulata (Billings). Shell substance corneous. 



The most interesting addition to our knowledge of the species is the discovery of the 

 presence of a narrow area on the ventral valve and a short pseudodeltidium, as shown in a 

 longitudinal section (PL II, figs. 3c-f). The existence of the area and pseudodeltidium in the 

 ventral valve of the variety swantonensis, the form studied by Beecher, and in the dorsal valve 

 of M. (P.) labradorica, was unknown at the time that Beecher [1891, p. 345] selected M. (P.) 

 labradorica swantonensis (see p. 344) as the simplest form or prototype (Paterina) , "preserving 

 throughout its development the main features of a protegulum, and showing no separate or 

 distinct stages of growth." 



The discovery of the area and pseudodeltidium refers the species and its varieties to the 

 genus Micromitra [Walcott, 1897b, p. 707]. 



The exact stratigraphic position of Locality 87 has not been made out, but from the 

 associated species of Agnostus and PtycTioparia, it is evidently to be referred to the Middle 

 Cambrian. 



This form owes its varietal name to its occurrence in the vicinity of Swanton, Vermont. 



Formation and locality. — Middle Cambrian: (87) Conglomeratic limestone 1 mile (1.6 km.) south-southwest 

 of Highgate Falls, Franklin County, Vermont. 



Lower Cambrian: (25a) Limestone on the Hall {Donaldson' s) farm, 2 miles (3.2 km.) east of Swanton; (319z) sandy 

 limestone 2.5 miles (4 km.) east of Swanton; (26) sandstone northeast of the Corman farm buildings, east of Highgate 

 Springs; and (319y) sandstone 2 miles (3.2 km.) east-southeast of Highgate Springs; all in Franklin County, Vermont. 



(319x) Limestone at the crossing of East Creek and Grove Street, 1.25 miles (2 km.) north of Rutland, Rutland 

 County, Vermont. 



Micromitra (Paterina) labradorica utahensis (Walcott). 



Text figure 24, page 350; Plate II, figures 8, 8a. 



Iphidella labradorica utahensis Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 306. (Characterized as a new variety.) 



The general form of this variety is much like that of Micromitra (Paterina) labradorica 

 (Bilhngs). It differs from it in the fine, threadlike, concentric striae of the outer surface, in 

 this respect approaching M. alabamaensis (Walcott) and M. (P.) superba (Walcott). During 

 the field season of 1906 fine specimens of this variety were found in the limestones 760 and 

 1,200 feet above the c(uartzitic sandstones referred to the Lower Cambrian. A ventral valve 

 6 mm. in width has a convex pseudodeltidium 1.25 mm. in length, with a width of 2.5 mm. at 

 its shghtly arched margins. The variety swantonensis also has a wide, convex pseudodeltidium 

 (PL II, figs. 3e, 3f). 



Formation and locality. — Middle Cambrian: (30c) About 1,050 feet (320 m.) above the Lower Cambrian and 

 3,350 feet (1,021.1 m.) below the Upper Cambrian in the shales forming Id of the Swasey formation [Walcott, 1908f, 

 p. 182], at the head of Dome Canyon, House Range [Walcott, 1908f, PL XIII], Millard County; (3d) concretionary lime- 

 stone about 100 feet (30.5 m.) above the quartzitic sandstones of the Cambrian, at Ophir, OquuTh Range, Tooele 

 County; (30p) about 125 feet (38 m.) above the Cambrian quartzitic sandstones, on the north side of Ogden Canyon, 



