158 PROCEEDINGS OF THE JSTATIONAL MUSEUM. vouxxii. 



0. (D.) mee(?siof Sillimaii's Fossil Mount also recalls 0. [D.) proavita 

 and 0. (D.) subquadrata, showing that the three probably belong to 

 one stock. 



Collectors.— J. N. Carpender and A. H. White. Cat. Nos. 28152,3, 

 U.S.lSr.M. A number of specimens are in the American 'Museum of 

 Natural History, which were collected by Mr. E. W. Porter. 



PLATYSTROPHIA BIFORATA (Schlotheim). 



Platystrophia Uforata Winchell and SchucherTj Geol. Minn., Ill, Pt. 1, 1893, 

 p. 455, pi. XXXIII, figs. 51-54. 



This ubiquitous Silurian species appears to be rare at the Frobisher 

 Bay locality, since but three specimens are present. These are small, 

 a condition in harmony with their Trenton age, and have short hinge 

 lines devoid of hinge extensions. The latter feature is best developed 

 in the upper or Richmond stage of the Cincinnatian group. 



Collectors.— S. N. Carpender and A. H. White. Cat. No. 28154, 

 U.S.N.M. A single specimen is in the collection of the American 

 Museum of Natural History. 



Family PORAMBONITIDJE Davidson. 



PARASTROPHIA HEMIPLICATA Hall. 

 Parastrophia hemiiJlicaia Schuchert, Bull. U. S. Geol. Surv., No. 87, 1897, p. 300. 



These small early pentameroids are under size in the Arctic locality, 

 but otherwise are more in harmony with examples from New York than 

 with those from Minnesota. 



Collector.— A. H. White. Cat. No. 28156, U.S.N.M. 



Order TELOTREMATA Beecher. 

 Family RHYNCHONELLID^ Gray. 



RHYNCHOTREMA MINNESOTENSIS (Sardeson). 



Ehynchotrema incequivalvis Winchell and Schuchert (part), Geol. Minn., Ill, 

 Pt. 1, 1893, p. 459, pi. XXXIV, figs. 9-11, 15-23 (not figs. 12-14, 24, 25). 



Rliynchonella mi/nnesoiensis Sardeson, Bull. Minn. Acad. Nat. Sci., Ill, 1892, p. 333, 

 pi. IV, figs. 21-23; Amer.Geol., XVIII, 1896, p. 184. 



The common Rhynclionella from the Birdseye or Lowville and Black 

 River stages, which is usually identified as B. increhescens Hall, is 

 always devoid of the concentric lamelhie so characteristic of R. incre- 

 besGens=R. incequivalvis of the Trenton stage. Occasional specimens 

 occur with a few of the lamellae near the anterior margin, but gen- 

 erally the shell is devoid of these, their places being occupied by very 

 fine, wavy, concentric lines. In higher beds, these fine lines develop 

 into stronger and more extended lamellie, which find their greatest 

 development in Rhynchotrema perlmnellosiim of the upper or Richmond 

 stage of the Cincinnatian group. 



! 



