BRACHIOPODA. 457 
Platystrophia biforata. ] 
equally protean are Leptena 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 /ynz,* 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 Hichwald. The above descrip- 
tion and figures haye 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 cost 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 cost 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 costz 
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—Chazy 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, lowa; 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 Clintun 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. Scofield, A. D. Meeds, HE. O. Ulrich and the 
writers. 
Mus. Rey. Nos. 2290, 4948, 5307, 5862, 7816-7828. 
*Terebratula lynx Bichwald. Skizze von Podolis, p. 202, 1830. 
**Pal, Ohio, vol. i, p. 114, figs. la-le, 1872. 
