536 GEOLOGY OF THE YELLOWSTONE NATIONAL PARK. 



Whitfield. 1 It differs in having the sinus less strongly developed, but is 

 otherwise indistinguishable. P. flemingi var bwrlingtonensis of the West, 

 however, differs from the true type seen at Burlington, Iowa, by being more 

 coarsely striate and less distinctly bilobed. In many respects P. semireticu- 

 latus of this region resembles P. newberryi var. annosus from the Waverly 

 sandstone of Ohio, but the striae in the latter, as seen in the figure, are more 

 angular, more irregular, and show a tendency to be discontinuous. 



Formation and locality: Madison limestone, near summit of ridge, 

 west end of Hunter Peak, Absaroka Range; Arnold Hague. East side of 

 Gallatin River, west of Electric Peak; divide between Gallatin River 

 and Panther Creek, Gallatin Range; east face of Antler Peak, Gallatin 

 Range; 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, bed 27, bed 28, bed 29, bed 31; J. P. Iddings 

 and W. H. Weed. South side of Gallatin Valley, bed 32 ; J. P. Iddings. 

 Northwest slope of Forellen Peak, Teton Range ; S. L. Penfield. Summit 

 of Three River Peak, Gallatin Range; J. P. Iddings. Crowfoot Ridge, 

 Gallatin Range, cherty limestone, top of bed 24; A. C. Gill. Head of 

 Conant Creek, Teton Range; W. H. Weed. Chouteau limestone. Black 

 Water, Saline County, Missouri; Chouteau Springs, Cooper County, 

 Missouri. 



Productus parviformis n. sp. 



PI. LXVIII, figs. 6a, 66, 6c, 6d. 



Productus parvus White, 1875; Wheeler's Expl. Surv. W. lOOtli Merid., Yol. IV, p. 83, 

 PI. V, figs. Ga, 6d; nou Productus parvus Meek and Wortlieu. 



Shell very small, somewhat wider than long. Surface ornamented by 

 fine, even, radiating strise, which sometimes exhibit a tendency to become 

 confluent, as in P. costatus. 



Ventral valve deeply arched, making considerably more than a semi- 

 circle; front view subquadrate, with nearly parallel sides and slightly curved 

 upper outline. About the beak are a few deep concentric wrinkles, and the 

 entire surface is crossed by fine concentric lines. Occasional spines of 

 comparatively large size are scattered over the surface, especially near the 

 anterior margin, on the heavier compound plications when present, 



1 King's U. S. Geol. Expl. 40th Par., Vol. IV, p. 265, PI. V, figs. 9-12. 



