PATERINID^. 347 



, MiCROMiTRA (Paterina) labradorica (Billings). 



Plate II, figures 2, 2a-f. 



Oholus lahradoricus Billings, 1861, Geol. Survey Canada, Paleozoic Fossils, vol. 1, p. 6, fig. 6. (Described as anew 



species. The specimen represented by fig. 6 is redrawn in this monograph, PI. II, fig. 2.) 

 Oholus lahradoricus Billings, 1861, Report on the Geology of Vermont, vol. 2, p. 946, fig. 345. (Copy of preceding 



reference.) 

 Oholus lahradoricus Billings, 1862, Report on the Economic Geology of Vermont, by Hager, p. 218, fig. 345. (Copy 



of preceding reference.) 

 Oholus lahradoricus Billings, 1863, Geol. Survey Canada, Fifteenth Rept. Progress, p. 284, fig. 291. (No text reference. 



Fig. 291 is copied from Billings, lS61b, fig. 6, p. 6.) 

 Iphidea lahradorica Billings, 1872, Canadian Naturalist, 2d ser., vol. 6, No. 4, p. 478. (Merely chances o-eneric 



reference.) 

 Iphidea lahradorica Billings, 1874, Geol. Survey Canada, Paleozoic Fossils, vol. 2, pt. 1, p. 76. (Copy of precedino- 



reference.) 

 Kutorgina lahradorica (Billings), Walcott (in part), 1886, Bull. U. S. Geol. Survey No. 30, p. 104, not PL IX, fio-s. 2 



2a-b. (Original description, Billings, 1861b, p. 6, copied and species discussed. The specimens figured, 



however, belong with Micromitr-a (Paterina) labradorica sivantonensis.) 

 Not Paterina lahradorica Beecher, 1891, Am. Jour. Sci., 3d ser., vol. 41, footnote, pp. 345-346, PI. XVII, figs. 1 and 2. 



(The specimens here referred to belong with Micromitra (Paterina) labradorica swantonensis .) 

 Kutorgina labradorica (Billings), Walcott, 1891, Tenth Ann. Rept. IT. S. Geol. Survey, p. 609, PL LXIX, figs. 3, 3a-b. 



(Mentions new locality. The specimens represented by figs. 3, 3a-b are redrawn in this monograph, PL II, 



figs. 2d, 2c, and 2a, respectively.) 

 Not Paterina labradorica Hall and Clarke, 1892, Eleventh Ann. Rept. State Geologist New York, for 1891, p. 247, 



fig. 258. (Genus Paterina described. Fig. 258 is copied from Walcott, 1886b, PL IX, figs. 21} and 2a, but the 



specimens belong with Micromitra (Paterina) lahradorica swantonensis.) 

 Iphidea labradorica (Billings), Schuchert (in part), 1897, Bull. U. S. Geol. Survey No. 87, p. 234. (Accepts Billings's 



reference of "Oholus lahradoricus" to Iphidea, but includes reference to specimens of Micromitra (Paterina) 



labradorica swantonensis.) 

 Iphidella lahradorica Walcott, 1905, Proc. U. S. Nat. Mus., vol. 28, p. 307. (Merely changes generic reference.) 



Ventral valve depressed, conical; the beak high and arched over the narrow area. Car- 

 dinal slopes flattened so as to form a narrow false area, which is clearly defined from the 

 curvature of the shell by a sharp angle ; pseudodeltidium unknown. 



Dorsal valve moderately convex, transverse, the hinge line being usually a little shorter 

 than the greatest width of the shell below. Beak small, slightly incurving over the pseudo- 

 deltidium. In some specimens there is a broad low mesial sinus, while in others this feature 

 is scarcely discernible. Cardinal slope nearly vertical, formiag a clearly defined narrow area, 

 broken at the center by a broad pseudodeltidium, the center of which is marked by a rather 

 broad, slight groove. The pseudodeltidium is well shown in two specimens, but the details 

 of its characters are not so well exhibited as in specimens of the dorsal valve of Micromitra 

 {IpMdella) pannula (White). Strise of growth cross the false area and pseudodeltidium. 



The surface is marked by rather fine concentric strife that are quite regular near the apex 

 of the shell, but less so outward toward the margin, as shown by the type specimens that 

 Wbiteaves kindly sent on to me for study. These also show fine, radiating strire that cross 

 the concentric strife and lines of growth, giving to the striae a slightly crenulated appearance 

 somewhat similar to that of Micromitra (Paterina) pros-pectensis (Walcott). Where the shell 

 is exfoliated, radiating strife are distmctly shown on the cast of the interior. On specimens 

 from the limestone carrying Olenellus, etc., at Topsail Head, Conception Bay, Ne^\^oundland, 

 the surface striae are less distinctly marked and the shells are smaller, but there appears to be 

 no specific difference between those from the Straits of Belleisle. Shell substance corneous. 



With a type specimen from L'Anse au Loup before me for comparison with the form from 

 the Lower Cambrian limestone east of Swanton, Vermont, I am still inclmed to distinguish the 

 latter as the variety swantonensis. The strife of the Swanton shells are usually finer and more 

 regular and the valves less transverse in proportion to the length. It is quite probable that 

 these differences would largely disappear on the comparison of a larger series of specimens 

 from the type locality, as there is a considerable range of variation among those from east of 

 Swanton and those from Topsail Head. 



