MOLLUSCA OF MICHIGAN— WALKER. 



491 



Fig. 78. Dentition of P. alternata. (Binney.) 

 KEY TO THE SPECIES OF PYRAMIDULA. 



I. Shell large, banded or flammulate. • 



a. Transversely banded solitaria. 



aa. Obliquely flammulate alternata. 



II. Shell smaller, unicolored, widely umbihcated, ribbed striate. 



a. Spire slightly elevated, obtuse, tooth on base of aperture, diam. 



8 mm perspectiva. 



aa. Spire more elevated, umbilicus narrower, no tooth in aperture, diam. 



6 mm cronkhitei anthonyi. 



aaa. Spire flat, prominently ribbed, minute asteriscus. 



Subgenus PATULA Held. 



Shell rather large and solid ; with convex spire and open umbilicus ; whorls 

 rounded or carinate at the periphery. Surface striate, ribbed-striate or spi- 

 rally ribbed; obliquely flamed, unicolored or spirally banded; lip thin, simple. 



PYRAMIDULA ALTERNATA (Say). 



Shell broadly umbilicated, orbic- 

 ularly depressed, thin, smoky horn- 

 colored with red, interrupted, 

 obliquely arranged patches and 

 spots; above closely rib-striate, 

 Fig. 79. P. alternata. (Binney.) Smoother below; whorls 5^, flat- 



tened, often angular at the periphery; aperture obhque. Innately rounded, 

 banded within; peristome simple, acute. 



Alt. 10, greater diam. 21, lesser 19 mm. 

 Helix alternata, Say, Nich. Encycl., pi. I., fig. 2, (1817). 



Fatula , W. G. Binney, Man. Am. Land Shells, 255, fig. 269, 



(1885). 



Helix , Sager, Doc. H. Rep. Mich., 1839, 420, separate, 14. 



-, Miles, Rep. Geol. Surv. Mich., 235, (1861). 



Anguspira -, Currier, Shell-bearing Moll. Mich., 5, (1868). 



Anguispira , DeCamp, Shell-bearing Moll. Mich., 6, (1881). 



Patula , Walker, Rev. Moll. Fauna Mich., 16, (1894). 



47 



