518 GEOLOGY OF THE YELLOWSTONE NATIONAL PAEK. 



Obverse: Midrib with two or three rows of small, circular, zocecial 

 apertures (exact number not ascertained). Branches with a double row of 

 alternate circular apertures, three to four opposite each fenestrate, making 

 about fifty in 1 cm. 



The genus Ptilopora ranges from the Hamilton to the base of the Coal 

 Measures, but, after occurring in the Hamilton, it does not reappear until the 

 Burlington, where a single species is known. The form from the Yellow- 

 stone National Park is distinct from anything yet described. 



Formation and locality : Madison limestone, Crowfoot Ridge, Gallatin 

 Range, top of bed 24; J. P. Iddings. 



STICTOPORELLA Ulrich, 1882. 

 Stictoporella (!) sp. 



By this name I wish to designate a frondose Bryozoan colony not 

 more than 1 mm. thick, but fully 2 mm. across, and apparently bifurcate, 

 or at all events bilobate. Both surfaces are alike, showing the circu- 

 lar apertures of numerous thick-walled pores, which are about 0.5 mm. 

 apart (measuring from the farthest walls), and without any conspicuous 

 order of arrangement. The intervening space is filled in with a large num- 

 ber of more or less circular mesopores, and the surface as a whole is raised 

 at intervals into low rounded monticules, which factor seems not to affect 

 the size or disposition of the zooidal openings. 



Formation and locality: Madison limestone, Crowfoot Ridge, Gallatin 

 Range, bed 28; J. P. Iddings and W. II. Weed. 



FENESTELLA Lonsdale, 1839. 



This genus is represented at several localities, and by a number 

 of forms, but as the material is both fragmentary and poorly preserved, 

 and when fragmentary can not always be distinguished from Archimedes, 

 nor even from Ptilopora, I have not attempted to make specific determi- 

 nations. 



At the locality on the east side of Lamar Valley, mouth of Soda Butte 

 Creek, Absaroka Range, there are probably two forms present. One has 

 very slender branches and thin dissepiments, leaving elongate angular 

 fenestrates from 2 to 3 mm. long and 0.5 mm. broad. This is a very regular 



