590 PROCEEDINGS OF THE ACADEMY OF 



when closely inspected with a powerful lens, give the tips of the tentacles a 

 ciliated appearance, resulting from the manner in which the bands are ar- 

 ranged. The bands are well-defined on the side toward the base of the ten- 

 tacle, but fading away into linear patches towards the tip. 



In half-grown specimens the tentacles are more slender and elongated, with 

 more numerous bands extending often beyond the middle towards the head. 

 Occasionally a specimen may be seen in which the tentacle terminates in a not 

 very well-defined bulb, approaching in appearance the eye-bearing tentacles 

 of Helices. 



The eye is situated on the apex of the tubercle placed against the posterior of 

 the base of the tentacle, and appears larger than in the preceding species, at 

 the same time giving a massive feature to the head. The pupil of the eye is a 

 well-defined black spot, surrounded by a bright yellowish surface, which is 

 again surrounded by a darker area extending down the sides of the tubercle. 

 The motions of the adult are slow, and seem to be regular and continuous ; 

 younger specimens move more rapidly, and are observed more frequently to 

 drag the shell by an interrupted motion than the adult ; but no elongation and 

 contraction of the foot has been noticed in either young or adult, as in the 

 preceding species. 



This species is found abundantly in the Mohawk River, in places where there 

 is considerable current, adhering to hard, dry banks, stones, sticks and aquatic 

 plants. It is seldom found associated with the preceding species their habits 

 being quite unlike. 



The following features of the two species above considered may suffice for 

 placing them apart in subgenera: 



1. The presence of a sinus or fold in the sides of the foot and neck of M. sub- 

 ularis and its absence in M. exilis. 



2. The extension of the anastomosing black lines from the margin of the 

 lateral portions of the foot upwards along the side of the neck in M. subularis, 

 and the restriction of these lines to a narrow zone along the lateral portions of the 

 foot of M. exilis. 



3. A well-defined dark band around the base of the tentacle in M. exilis ; not 

 observable, or at most only faintly indicated, in M. subularis. 



Cyclostoma lapidakia, Say. 



The soft parts of this animal have been observed, and notes in relation there- 

 to have appeared in the Proceedings of the Boston Soc. Nat. Hist. It may be 

 well to apply here a few inadvertent omissions. 



The rostrum is proportionally larger than in Amnicola and has the appear- 

 ance of Melania, being marked with well-defined transverse black lines. The 

 tentacles are proportionately large, and, instead of being directed obliquely for- 

 ward, droop and form an angle near their middle. The eye, instead of being 

 placed in a tubercle at the base of the tentacle, is placed in a tubercle, sur- 

 rounded by a well-defined and elevated process, presenting the appearance of 

 a cup or ring around the eye tubercle, which ring at its anterior side unites 

 with the base of the tentacle. The motions of the animal are entirely unlike 

 Amnicola (in which genus this mollusc has been included by late writers who 

 have examined the shell only,) and are very much like the movements of 

 Melania subularis, only that it exhibits more uniformly the expansions and 

 contractions of the foot in progressing, and also exhibits a very positive halt 

 at each movement. Its progress in moving is slow and irregular. The shell 

 is not carried obliquely erect as in Amnicola and Paludina, but drags behind 

 the foot as in Melania subularis, and is hitched along in the same manner. 

 A figure of the soft parts of Truncatella in the Supplement to Terr. Moll, by 

 W. G. Binney is a better illustration of this mollusc than any figure of Amni- 

 cola yet published. 



This resemblance, together with an agreement in habit with Truncatella, 



[Dec 



