472 



MICHIGAN SURVEY, 1905. 



Superfamily AGNATHOMORPHA. 



Family CIRCINARIID/C. 



Animal naked, with an internal shell or bearing an external, heliciformr 

 shell. Foot without pedal grooves or caudal mucus pore. Jaw ribless, 

 with or wdthout a median projection on the cutting margin. Radula with 

 arcuate rows of teeth. Centrals short, rudimentary; marginals aculeate, 

 Avith narroAV basal plates. 



Genus CIRCINARIA (Beck) Pilsbry. 



Shell thin, widely umbilicated, depressed, striate or wrinkled; color uni- 

 form; whorls 4^-5, the last broad, depressed, moderately deflexed in front; 

 aperture obhquely ovate; peristome somewhat thickened or expanded, the 

 margins approximating, the basal shortly reflexed. 



Animal heliciform; mantle posterior covered with 

 \ a shell; eye-peduncles long and slender; foot nar- 



row, twice as long as diameter of shell, tail pointed, 

 scarcely reaching behind the shell; respiratory and 

 anal orifices on the right of the mantle under the 

 Fig. 25. Anunai^of c.conca.a. p^^stome of the shell; generative orifice behind the 

 right eye peduncle; no distinct locomotive disk or caudal mucus pore. 

 ^^^ Jaw crescentic, ends sharply pointed, anterior surface striated; cut- 

 Fig. 26. ting margin smooth, with a median projection. 

 c ^colcfva Radula with the rows of teeth arranged en chevron. Centrals very 

 (Binney.) Small, basal plate triangular, apex pointed forward, more or less 

 truncated and incurved; lower lateral angles somewhat expanded, base in- 

 curved, uni or tricuspid; laterals wanting; marginals arculeate with long: 

 narrow basal plates. 



Fig. 



Dentition of C. concava. (Binney.) 



Fig. 28. C. concava. 

 (Binney.) 



Helix concava 

 Macrocylis 



CIRCINARIA CONCAVA (Say). 



Shell depressed, w^hitish or greenish- white horn-color ; whorls 

 above flattened; rounded below; finely striate, outer whorl ex- 

 ]:>anding slightly towards the aperture; suture rather deeply 

 impressed; umbihcus wide and deep; aperture rounded, some- 

 ^ what flattened above ; its edge frequently tinged with reddish 

 brown; peristome slightly thickened and subreflected below. 



Alt. 8, greater diam. 17, lesser 14 mm. 



Say, Jour. A. N. S. P., II., 159, (1821). 



W. G. Binnev, Man. Am. Land Shells, 199, fig. 209, 



(1885). 



