LOWER CARBONIFEROUS FOSSILS. 549 



bed 27, upper part of bed 27, bed 28, bed 31; J. P. Iddings and W, H. 

 Weed. Pass between Fox and Mink creeks, west of Two Ocean Plateau; 

 Arnold Hague. East slope of Survey Peak, Teton Range ; south of Forel- 

 len Peak, Teton Range; northwest slope of same; S. L. Penfield. Antler 

 Peak, Gallatin Range; west of same; A. C. Grill. Summit of peak west 

 of Antler Peak, Gallatin Range; south slope of same; summit of Three River 

 Peak, Gallatin Range ; J. P. Iddings. South slope of Quadrant Mountain, 

 Gallatin Range; A.C.Gill. South base of same ; J. P. Iddings. North of 

 Bighorn Pass, Gallatin Range; Crowfoot Ridge, Gallatin Range, bed 24; 

 A. C. Gill. Bighorn Pass, Gallatin Range ; J. P. Iddings. Head of Conaut 

 Creek, Teton Range; north end of Teton Range, north of Owl Creek; east 

 side of Lamar Valle}'-, mouth of Soda Butte Creek, Absaroka Range; 

 W. H. Weed. Limestone bluff south side of Soda Butte Creek, north- 

 west of Abiathar Peak, Absaroka Range; J. P. Iddings. North side 

 of north fork of Mill Creek, Snowy Range; J. P. Iddings and Louis 

 V. Pirsson. Waverly age, Cuyahoga Falls, Richfield, Lodi, Bagdad, etc, 

 Ohio; Black Hills, Dakota; Wasatch Range, Utah; Mountain Spring, 



Nevada. 



Spirifer centronatus var. semikurcatus n. var. 



PL LXX, fig. 4«. 



This form is related to S. centronatus and to S. mesicostalis, standing about 

 midway between them. It seems to me to be sufficiently out of the ranere 

 of ordinary variations of 8. centronatus to be described as a distinct variety. 



It is of the imbrex type, semielliptical in outline, fold and sinus 

 strongly expressed ; surface ornamented with regular imbricating growth 

 lines and strong radiating ribs. Of the latter there are ten or eleven upon 

 the wings and two somewhat larger ones upon the median fold. These, 

 however, show a constant tendency to bifurcate, which often results in the 

 formation of four plications; but the median furrow of the fold is stronger 

 than the two others. Length of the dorsal valve is 30.5 mm. transvessel v ; 

 longitudinally, 12.5 mm. 



The dorsal shown by PI. LXX, fig. 4a, can be almost exactly mated in 

 size, in shape, and in the number, size and distribution of the plications bv 

 specimens of S. mesicostalis. This, however, is rather small for mesicostalis, 

 and 1 have not observed, in a large series of this species, any tendency 

 toward bifurcation in the two plications on the fold. Compared with S. 



