554 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Mature specimens can scarcely be mistaken for anything else in the 

 same beds. The smooth surface and area with triangular foramen would 

 suffice to distinguish even young shells from C. crassicardinalis, which they 

 most resemble, but when these characters are obscured the prominent beak 

 and mesial sulcus of the ventral valve are diagnostic. There is some simi- 

 larity with Spirifer (Martinia) glaber Martin, to which I believe this type 

 to have been usually referred. The produced and overhanging beak and 

 large area of M. rostrata are well-marked specific characters. The fold and 

 sinus of M. glabra are stronger than the same features of M. rostrata, where, 

 in fact, they are but slightly developed, and often exhibit a tendency to 

 bifurcate, manifested by a median sulcus and ridge of more or less depth, 

 never seen in the latter. 



The synonymy of this form includes, so far as I am aware, besides S. 

 glaber, of various authors, only Athyris plauosulcata (f) Hall and Whitfield 

 (non Phillips), figured in King's U. S. Expl. 40th Par., Vol. IV, p. 257, PL 

 IV, fig. 10, which appears to be a young specimen of M. rostrata. Width 

 of large specimen, ventral valve, 38 mm.; length, 35.5 mm. Width of 

 medium-sized specimen, ventral valve, 29 mm.; length, 25.5 mm. Width 

 of large specimen, dorsal valve, 51 mm.; length, 34.5 mm. Width of me- 

 dium-sized specimen, dorsal valve, 29 mm.; length, 23.5 mm. 



Formation and locality: Madison limestone, east side of Gallatin River, 

 west of Electric Peak; G. M. Wright. Amphitheater west of Bannock 

 Peak, Gallatin Range, bed 26; W. H. Weed. Crowfoot Ridge, Gallatin 

 Range, top of bed 25; J. P. Iddings and G. M. Wright. Same, lower 

 part of bed 27, bed 31; J. P. Iddings and W. H. Weed. South side of 

 Gallatin Valley, bed 32; J. P. Iddings. West of Antler Peak, Gallatin 

 Range; A. C. Gill. South slope of peak west of Antler Peak, Gallatin 

 Range ; summit of Three River Peak, Gallatin Range ; J. P. Iddings. South 

 slope of Quadrant Mountain, Gallatin Range; north of Bighorn Pass, Gal- 

 latin Range; A. C. Gill. North of Owl Creek, northeast slope of Teton 

 Range; W. H. Weed. Limestone bluff south side of Soda Butte Creek, 

 northwest of Abiathar Peak, Absaroka Range; J. P. Iddings. 



