98 PALEONTOLOGY OF NEW YORK. 



both valves, and it would be difficult to indicate essential differences in the 

 general form and proportions of this species and /. bella* 



Notwithstanding the fact that our knowledge of these shells is so circum- 

 scribed, certain of their features are of definite generic value. 



The apical foramen indicates the close alliance of the genus 

 with AcROTRETA and Acrothele, and may be considered as an inter- 

 mediate stage in the forward progress of the pedicle-aperture from 

 its intermarginal position in the linguloids and oboloids, to its ^'^j.^^*; efLmNGs'""' - 

 excentric position and tubular character in Schizambon. The flattened subapical 

 slope is a feature also seen in Acrotreta, while the convex foraminal covering 

 on this area, which gives to the shell an appearance so suggestive of Orthisina, 

 is found in the inarticulate brachiopods only here and in Volborthia. The shell- 

 substance is corneous, apparently consisting of but few layers. 



The originals of Mr. Billings' I. bella were from Trois Pistoles, near Quebec ; 

 " a closely allied species of the same genus occurs in the primordial limestone 

 at Topsail Head, Conception Bay, Newfoundland" (Billings, loc. cit.). The 

 specimen here figured on Plate IV (figs. 8, 9), is from Georgia, Vermont. 

 We have before us specimens of a species from the Grand Canon, Arizona 

 (Tonto group of Walcott = Potsdam sandstone?), which bears a more promi- 

 nent areal ridge than /. bella, and has the cardinal edge elevated above the 

 rest of the margin of the valve, a feature strongly marked in Linnarsson's 

 species, /. ornatella. 



Genus ACROTHELE, LinnarssoxN. 1876. 



PLATE m, FIGS. 25-31. 



1868. Lingula, Haktt. Dawson's Acadian Geology, Second Edition, p. 644. 



1876. Acrotliele, Linnaksson. On the Bi-acbiopoda of the Paradoxides Beds of Sweden, p. 20. 



1879. Obolus?, Barkabdk. Systeme Silui-ien du Centre de la Boheme, vol. v, pi. 102, %. vii. 



1879. Blscina, Bakrande. Systeme Silurien du Centre de la Boheme, vol. v, pi. 110, fig-, vii. 



1881. Acrotliele, White. Proceedings United States National Museum, vol. iii, p. 47. 



1883. Acrotliele, Davidson. British Silurian Brachiopoda, Supplement, p. 214. 



? 1884. j4e?'oi7ie/e .9, Walcott. Palseontology Eureka District, p. 14. 



1SS4. Acrotliele, Walcott. Bulletin No. 10, United States Geological Survey, p. 15. 



* IMr. Walcott has pi-omised additional details in regard to this genus (Bulletin No. 30, U. S. Geological 

 Survey, p. 100), which will be looked for with intei'est. 



