634 CAMBRIAN BRACHIOPODA. 



far to the south in the Appalachian province, A. hellula Walcott; and to the north in Pennsyl- 

 Tania, A. yorltensis Walcott. The general distribution of species is given in the table (p. 105) 

 and the details of each species under the specific description. 



StratigrapJiic range. — Acrothele is represented by eight species and one variety in the 

 upper portion of the liower Cambrian in association with Olenellus or alhed forms of trilobites, 

 but in no instance has it been found low down in the Lower Cambrian. In the Middle Cambrian 

 twenty-one species and six varieties occur, and there the genus attained its widest distribution 

 and greatest development. One species, A. horgholmensis Walcott, occurs in strata of the 

 Geratofyge zone, and three species in Lower Ordovician formations. Of the latter, A. ceratopy- 

 garum is not a typical form of Acrothele. (See p. 640.) 



Acrothele artemis Walcott. 



Text figure 54. 



Acrothele artemis Walcott, 1908, Smithsonian Misc. Coll., vol. 53, No. 3, p. 82, PI. VIII, fig. 10. (Described and 

 discussed as below as a new species. Fig. 10 is copied in this monograph as fig. 54.) 



General form of ventral valve moderately convex; subcircular and somewhat obtusely 



acuminate in outline; apex near the posterior margin; pedicle opening urLkno^vn, but from the 



occurrence of a small boss on the inside of the shell beneath the 



apex it was probably of the same character as in closely related 



species. 



Surface marked by concentric lines and small ridges of growth, 

 and an irregular system of fine granules on the concentric ridges; 

 in the lower interspaces there is an irregular distribution of very 

 minute inosculating ridges that, with the tubercles, form a surface 

 independent of the concentric growth lines. The shell is built up 

 i-iGUEE 5i.-Acrotheie artemis Walcott. of numerous lamellse beneath the outer surface layer and appears 



A, A', Ventral valve with the apex , , ipiij.r'Ti 



broken. The specimen is from Lo- to liave been comeous, or composcd 01 phosphatc or ume and 



cality 5b, Middle Cambrian lime- chitin. 



stones in Twomile Canyon, south- mi i j. i ii i i ii, J 'l-H « in j.1 



east of Maiade, Oneida County, I he largest shcll has a length and Width ot 10 mm.; the apex 



Idaho, (u. s. Nat. Mus. Cat. No. ig about 2 mm. from the posterior margin; dorsal valve unknown. 



,. . 51969.) The figure is copied from ^v ,• nii ■ • t i • c a ,t i 



Walcott, i908d, PI. vm, fig. 10. Observations. — ims species resembles m iorm Acrothele pnma 



costata (Matthew) (PI. LXI, figs. 4 and 4a), and both species have 

 a granular surface. The latter species, however, has a thinner sheU, and its surface is marked 

 by much larger granules. I know of no other closely related species. 



Formation and locality. — Middle Cambrian: (5b) Dark blue-gray Langston limestone [Walcott, 19081, p. 198], 

 just above the Cambrian quartzitic sandstones, north side of Twomile Canyon, near its mouth, 2 miles (3.2 km.) south- 

 east of Maiade, Oneida County, Idaho. 



Acrothele avia Matthew. 

 Plate LXI, figures 7, 7a-b; Plate LXII, figures 1, la-k. 



Acrothele avia Matthew, 1899, Bull. Nat. Hist. Soc. New Brunswick, vol. 4, pt. 3, No. 18, pp. 202-203, PI. Ill, figs, 

 la-h. (Described as a new species. The specimens represented by figs. Ic and If are redrawn in this mono- 

 graph, PI. LXI, figs. 7a and 7b, respectively.) 



Acrothele avia Matthew, 1902, idem, pt. 5, No. 20, pp. 396-398, PI. XVI, figs. 7a-b; PI. XVII, figs, la-f and 2a-b. 

 (Described and discussed. PI. XVII, figs, la-f, and PI. XVI, figs. 7a-b, are copied fi-om Matthew, 1899b, PL 

 III, figs. la-h. The specimens represented by figs. 2a and 2b are redrawn in this monograph, PI. LXI, fig. 7, 

 and PL LXII, fig. li, respectively.) 



Acrothele abavia Matthew, 1902, idem, pp. 398-400, PL XVI, figs. 3a-d and 4a-b. (Described and discussed as a new 

 species.) 



Acrothele avia Matthew, 1903, Geol. Survey Canada, Kept. Cambrian Kocks Cape Breton, p. 55. (Notes on orienta- 

 tion of valves.) 



