500 



MICHIGAN SURVEY, 1905. 



Fig. 103. Jaw of S. retusn. 



Fig. 104. Jaw of S. ovalis. 



Fig. 105. Jaw of S. avara. 



Radiila with, centrals tricuspid; laterals bicuspid or tricuspid; marginals 

 short, serriform; the centre of the lower edge of the basal plates of the cen- 

 trals and inner lower lateral angle of the basal plates of the laterals and 

 marginals cut away. The reflection of the teeth is small in proportion to 

 the size of the basal plates. 



Fig. 106. Dentition of S. retusa (Binney.) 

 KEY TO THE SPECIES OF SUCCINEA. 



I. Spire very small, aperture very large, more than one-half of entire 



length of shell. 



a. Body whorl large, expanded, aperture broadly oval obliqua. 



aa. Body w^horl compressed, elongate, aperture elongated retusa. 



II. Spire prominent, acute, whorls very convex, suture deep, aperture 



rounded at both extremities, ovate, hirsute when young avara. 



SUCCINEA RETUSA Lea. 



Fig. 107. S. retusa. 

 (Lea.) 



Fig. 108. 



S. calumefensis. X2. 

 (Calkins.) 



Fig. 109. S. retusa. 

 (Binney.) 



Shell ovate, somewhat conic, very thin, pellucid, light yellow or grayish, 

 liorn-color; shining, very minutely striate; whorls 3, the last compressed 

 and elongated; spire short but acute; suture impressed; aperture elongated, 

 more or less patulous, expanding anteriorly, 

 i Alt. 15, of aperture, 10 mm. 

 Succinea retusa, Lea, Trans. Am. Phil. Soc, V., 117, pi. XIX,, fig. 86, 



(1837). 

 ovalis, W. G. Binney, Man. Am. Land Shells, 338, fig. 368, (1885). 



