522 MOLLUSCA 



narrow; umbilicus closed; height 14 mm.; diameter 23 mm.; America 

 west of the Alleghenies and south of central Michigan. 



P. thyroides (Say) (Fig. 806). Shell depressed, thin, yellowish- 

 brown; aperture with a prominent white tooth on parietal wall; umbili- 

 cus narrow and partially covered by the reflected peri- 

 stome ; height 18 mm. ; diameter 22 mm. : eastern and 

 ?So«^iail) central America. 



Family 7. ENDODONTIDAE. 

 Shell conical or depressed, ribbed or striated, usually 

 Avith brown markings, and with open umbilicus; lip thin 

 and sharp, usually without teeth: 4 American genera. 

 Key to the genera of Endodontidae here described: 

 (ii Jaw composed of a single piece. 



Pofygyra ^^ Spire raised, but low 1. Pybamidula 



thyroides h^ Shell discoid 2. Helicodiscus 



(Baker). ^^ j^^ composed of numerous overlapping pieces; shell 



heliciform (Fig. 772) 3. Punctum 



1. Pyramidula Fitzinger. Shell with 5 or 6 whorls and a wide 

 umbilicus; aperture rounded and large, usually without teeth; foot with 

 marginal grooves which meet behind; dart sac, mucous genital glands, 

 and flagellum absent; jaw not ribbed, but striated: cosmopolitan; about 

 12 American species. 



Key to the species of Pyramidula here described : 



Ox Shell without prominent transverse ribs. 

 6i Shell color with markings. 



Ci Shell with 2 or 3 revolving bands P. solitaria 



Ca Shell with broken, irregular transverse bands. P. alternata 



62 Shell color plain P. perspectiva 



aa Shell with prominent transverse ribs P. asteriscus 



P. solitaria (Say) (Fig. 807). Shell elevated, white 

 or reddish, striped with 2 or 3 broad revolving brown Fig. 807 



bands; height 19 mm.; diameter 25 mm.: America, north ^solitaria 



( I5aker) 



of the Ohio River; Oregon and Washington. 



P. alternata (Say). Shell depressed, yellowish, with oblique and 

 broken red bands; height 10 mm.; diameter 21 mm.: eastern and central 

 America ; abundant in decaying logs and other damp places ; gregarious. 



P. perspectiva (Say). Shell flattened, thin, brownish; aperture 

 small, often with a single small tooth; height 3 mm.; diameter 8 mm.: 

 eastern and central America, but not east of the Alleghenies north of 

 Maryland. 



P. asteriscus (Morse). Shell veiy flat, with 25 or 30 prominent 

 transverse ribs on the Avhorls; height .5 mm.; diameter 1.5 mm.: New 

 England and Canada; California. 



