PLEUROCERA. 



G3 



The deep sulcus which distinguishes Mr. Say's 3feL canalicu- 

 lata, in its typical form, shades off so gradually into a smooth, 

 flattened surlace, that not only is it difficult to arrange the 

 species of this group, but it is even doubtful whether many of 

 the species which are placed in other groups are really distinct. 

 Especially, may it be doubted whether the small shells recently 

 described by Mr. Lea under Fig. 120. Fig. iis. Fig. 117. ig.iio. 

 the names of bivittatum, pami- 

 lum, simplex, etc., are distinct 

 from the young of canalicula- 

 tum. 



Mr. Say describes the young 

 shell oH canal iculata as Melania 

 conica. It is differently formed 

 from the adult shell and does 

 not possess the sulcated body- 

 whorl. The illustrations of 

 this species, all drawn from 

 specimens, exhibit the various 

 stages of growth, etc. 



Fig. 116 is a tall, slender 

 form from the Ohio River, 

 scarcely sulcate. No. 117 represents a stunted specimen also 

 from the Ohio. No. 119 is from Tennessee River. No. 120 is 

 a quite young shell from the Falls of the Ohio. No. 122 is a 

 heavy northwestern form ; the specimen probably came from the 

 interior of Ohio. No. 121, a beautiful sharply sculptured form, 

 is from Tennessee. Nos. 117, 118, 119 represent the M. conica 

 of Say. It will be seen that there is much variation of form in 

 this species ; so the color also varies from a light green and 

 yellow to a dark brown or nearl}' black and is either uniform or 

 banded. The area of geographical distribution is very great, 

 extending from the interior of Ohio to Alabama and through 

 Indiana and Illinois. 



The following is Mr. Say's description of 



M. conica. — Shell conic, rapidly attenuating to an acute apex, very 

 slightly wrinkled, olivaceous ; suture not deeply impressed ; volutions 

 seven or eight; aperture oblique, equalling the second, third, and 

 fourth whorls conjunctly. 



T'ar. A. With from one to three revolving, rufous or blackish lines. 



