PATERINID^. 333 



Micromitra Meek, 1873, Sixth Ann. Rept. V. S. Geol. and Geog. Survey Terr, for 1872, p. 479. (Suggests Micromitra as 



anewgenerionamefor"Jp/!trfea(?.?)scMZpfiMs" if that species should prove to belong to a new genus. This refer- 

 ence is quoted in this monograph, p. 334.) 

 Iphidea Billings, 1874, Geol. Survey Canada, Paleozoic Fossils, vol. 2, pt. 1, p. 76. (Copied from Billings, 1872b, 



pp. 477^78.) 

 Iphidea Billings, Linnarsson, 1876, Bihang till K. svensk. Vet.-Akad. Handl., Bd. 3, No. 12, p. 26. (Mentioned in 



English in the discussion of "Iphidea ornatella.") 

 Iphidea Billings, Ball, 1877, Bull. U. S. Nat. Mus., No. 8, p. 39. (Mentioned.) 

 Iphidea Billings, Walcott, 1886, Bull. U. S. Geol. Survey No. 80, pp. 100-101. (Copies the original description, BU- 



lings, 1872b, pp. 477-478, of the type species {"Iphidea bella") and discusses genus.) 

 Kutorgina Walcott (in part), [not Billings], 1886, Idem, pp. 101-102. (Genus Kutorgina described, but descrip- 

 tion also includes reference to specimens now referred to Micromitra, Micromitra (Paterina), and Micromitra 



{Iphidella) .) 

 Iphidea Billings, Oehlert, 1887, Manuel de conchyliologie, by Fischer, p. 1270. (Described in French.) 

 flphidea Billings, Hall and Clarke (in part), 1892, Eleventh Ann. Kept. State Geologist New York for 1891, p. 249 



(Described, but accompanied by figures of specimens belonging with the subgenus Paterina.) 

 flphidea Billings, Hall and Clarke (in part), 1892, Forty-fifth Ann. Rept. New York State Mus. for 1891, p. 565 



(Copy of preceding reference.) 

 Kutorgina Walcott, Hall and Clarke (in part), 1892, Nat. Hist. New York, Paleontology, vol. 8, pt. 1, pp. 90-94 



(Copies Walcott's description, 1886b, pp. 101-102, and discusses genus, but description and discussion also 



include reference to specimens now referred to Micromitra, Micromitra (Paterina), Micromitra {Iphidella), Pro- 



torthis, and Billing sella.) 

 Iphidea Billings, Hall and Clarke, 1892, idem, pp. 97-98. (Copies the original description, Billings, 1872b, pp. 



477-478, of the type species {"Iphidea bella") and discusses genus.) 

 Iphidea Billings, Walcott (in part), 1897, Proc. U. S. Nat. Mus., vol. 19, pp. 707-711. (Discussed. The genus includes 



species now referred to Micromitra, Micromitra {Paterina), and Micromitra (Iphidella) .) 

 Iphidea Billings, Schuchekt (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 233. (Merely refers Micromitra and 



Paterina to Iphidea.) 

 Iphidea Billings, Walcott, 1899, Mon. U. S. Geol. Survey, vol. 32, pt. 2, pp. 447-448. (Mentioned in discussion of 



" Iphidea sculptilis ." ) 

 Iphidella Walcott (in part), 1905, Proc. U. S. Nat. Mus., vol. 28, p. 304. (Merely proposed to replace Iphidea, but 



includes reference to specimens belonging with Micromitra, Micromitra (Paterina), and Micromitra (Iphidella).) 

 Paterina (Micromitra) (Meek), Schuchert, 1905, Am. Jour. Sci., 4th ser., vol. 19, p. 329. (Suggests that Micromitra 



be used in a subgeneric sense, under Paterina, for the forms typified by Micromitra sculptilis.) 

 Not Iphidea Grabau and Shimer, 1907, North American Index Fossils, vol. 1, p. 201. (Described, but the species 



placed under it belong with the subgenera Paterina and Iphidella.) 

 Micromitra Meek, Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 4, PI. XI, and pp. 142 and 143. (Classification 



of genus.) 



Ventral valve conical (Micromitra (Paterina) etheridgei (Tate), PI. Ill, fig. 10) to depressed 

 conical (M. (P.) labradorica (Billings), PI. II, fig. 2), with the beak curving more or less over a 

 false area which is divided midway by a triangular fissure that may be covered almost entirely 

 {M. (P.) superha (Walcott), PI. II, fig. 1) or only in part (Micromitra (Iphidella) ornatella (Lin- 

 narsson), PI. Ill, fig. 6) by a convex pseudodeltidium. 



Dorsal valve slightly to moderately convex. Beak small and usually curved a little over 

 a low area ( Micromitra pealei (Walcott) , PI. Ill, fig. 3e') that has a rather broad pseudodeltidium. 



Surface marked by concentric lines of growth and fine radiating stride ( Micromitra (Paterina) 

 labradorica (Billings)) ; crenulated concentric striae that give a more or less distinctly crenu- 

 lated appearance to the surface (Micromitra sculptilis (Meek)); and strongly crenulated concen- 

 tric striae forming a network of raised, obliquely arranged lines that divide the surface into 

 minute pits (Micromitra (Iphidella) pannula (Wliite)). 



Shell substance corneous. Shell built up of thin layers or lameUse that are more or less 

 obhque to the outer surface. 



Very little is known of the interior of the valves. The ventral valve of Micromitra (Pater- 

 ina) labradorica (Billings) (PL II, fig. 2c) has a few lines or ridges that radiate from the beak 

 very much as in Kutorgina (PI. V, fig. 1). The dorsal valve also shows radiating ridges (Micro- 

 mitra (Iphidella) ornatella (Linnarsson) PI. Ill, fig. 6d), and in addition an exfoliated shell of 

 M. (I.) pannula ophirensis Walcott shows a median ridge, the base of the main vascular sinuses, 

 and two central muscle scars (PI. IV, fig. 4e). 



Type.— Iphidea (?f) sculptilis Meek [1873, p. 479]. 



