190 BULLETIN OF THE 



Triodopsis obstricta, SAY. 

 appressa, SAY. 



It is quoted by Von Martens from the banks of the Columbia River, but 

 from drawings and description of the single specimen found by Kraus, kindly 

 sent me by Dr. Von Martens, it appears that the species was confounded with 

 flattened forms of Mullani or devius. 



Triodopsis inflecta, SAY. 



A depauperated form of this species is about being described and figured as 

 T. edentala by Mr. F. A. Sampson. 



Triodopsis Rugeli, SHUTTLEWORTH. 

 tridentata, SAY. 



The deformed specimen figured is one of appressa, not of this species. 



Triodopsis fallax, SAY. 



introferens, BLAND. 



Van Nostrandi, BLAND. 



Also, Jacksonville, Florida. 



Mesodon major, BINNEY. 



On Plate I. Fig. 2, I have figured the dentition of an individual of this spe- 

 cies differing from that figured in Vol. V. Plate VIII. Fig. G, by wanting the 



side cusps and cutting points of the central and 

 first lateral teeth. The individual from which the 

 lingual was extracted is labelled B in the collec- 

 tion given by me to the United States National 

 Museum. Fig. 3 gives an outer lateral of the 

 same membrane, on which the side cusp and cut- 

 ting point are present. Fig. 1 gives a central tooth 

 with side cusps and cutting points from the mem- 

 brane of the specimen labelled A. 



The figures show a larger range of variation in 



the dentition of individuals of the same species than would have been antici- 

 pated. (See also M. Andrewsi.) 



Mesodon albolabris, SAY. 



Andrewsi, AY. G. B. 



In the Manual of American Land Shells, p. 302, I have described and fig- 

 ured specimens of a larger form of this species, which would be called major 

 by most collectors, but which has the genitalia and lingual dentition of An- 

 drewsi. (See figure above.) 



The penis sac of Andrewsi was described by me as constricted in the middle. 

 Further study has convinced me that it is rather twisted than constricted. 

 On Plate I. Fig. 4, I give a figure of the genitalia to show this ; and in Fig. 5, 

 the penis sac of still another individual. 



