BRACHIOPODA. 457 



Platystropliia blforata.] 



equally protean are Leptcena rhomboidalis, which extends from the Trenton into the 

 Waverly, i. e., from the Lower Silurian to the base of the Carboniferous; Atrypa 

 reticularis, extending throughout the Silurian and Devonian; Orthis testudinaria, from 

 the Chazy to the top of the Lower Silurian; Plectambonites sericea, from the Trenton 

 to the Clinton, i. e., from the Lower Silurian to the Silurian. 



The references treating strictly of the large and globose variety lynx,* as defined 

 by Meek,** are not given in the above synonomy, since that variety is regarded as 

 amply distinct for easy recognition. It is not known to occur in the northwest. 



M. de Verneuil, in a foot note appended to the description of Spirifer sheppardi 

 Castelnau, states that it is identical with Spirifer lynx Eichwald. The above descrip- 

 tion and figures have been studied by the writers, who find them to agree with 

 examples here referred to P. biforata. If desirable to separate American specimens 

 under another specific term, because they have, as a rule, a less number of costae in 

 the sinus and fold than European examples of P. biforata, the name given by Castel- 

 nau will have precedence. 



Platystrophia biforata is sparingly found near the top of the Trenton shales and 

 becomes one of the characteristic fossils of the Galena shales in Minnesota. Nearly 

 all the specimens seen have three plications in the sinus, with four on the fold, while 

 an individual is rarely found with one more or one less. In other regions, the 

 number in the sinus is also usually three, while occasionally only one, five, or even 

 six are developed. Commonly there are from twelve to sixteen costae on each side 

 of the fold and sinus. More rarely a specimen is found with ten, while several 

 immature individuals have only from five to seven. Some of the plications are 

 seen to terminate along the cardinal area, and since increase in number of costse 

 very rarely takes place on the lateral slopes by bifurcation or otherwise, new 

 ones may be added along the postero-lateral margins as the length of the hinge is 

 increased. 



Formation and locality. Cha/y group near Montreal, Canada. Common in the Trenton of New 

 York, Canada, Kentucky, Tennessee, and rare in this horizon in the northwest. In the lower portion of 

 the Galena formation it is common at many localities in Goodhue, Olmsted and Fillmore counties, Min- 

 nesota; Decorah and Dubuque, Iowa; Neenah and Oshkosh, Wisconsin, and, according to Castelnau, at 

 the mouth of Menominee river, Green Bay. In the Cincinnati group of the Ohio valley; Nashville, Ten- 

 nessee; Iron Ridge, Wisconsin; Graf, Iowa, and Silver City, New Mexico. In the Clinton and Niagara 

 formations of Ohio, New York, Canada and Anticosti. It is also a common fossil in the Lower Silurian 

 and Silurian in England, Scotland, Ireland, Gotland, Scandinavia, Oeland and Russia. 



Collectors. Miss Cora E. Goode, Dr. Sandberg, W. H. Scofleld, A. D. Meeds, E. O. Ulrich and the 

 writers. 



Mus. Beg. Nos. 2290, 4948, 5307, 5862, 7816-7828. 



Terebratuta lynjc Eichwald. Skiz/.e von PoilolN. p. aw, 

 "Pal. Ohio. vol. i, p, 114, tigs, la-le, 1872. 



