NATURAL SCIENCES OP PHILADELPHIA. 589 



apparent gliding motion of the whole foot ; more usually the progressive 

 movements are an alternate expansion and contraction of the foot. 



This Melania abounds in the Mohawk River, preferring sloping, muddy hanks 

 in eddies, where there is little current. 



Melania exilis, Haldeman. 



The shells of this species are quite variable in form and color, so much so 

 as to have drawn from a distinguished zoologist the inquiry if they might not 

 be more than one species. 



Some are elongated and slender, with scarcely any angularity on the larger 

 whorls below the carinated apicial whorls ; others are more robust, with a 

 wider apicial angle, with a tendency to form gibbous enlargements of the last 

 whorl. In these there is an obsolete angle between the base of the shell and 

 the surface of the spire. The soft parts present some diversity of color, as is 

 the case with all the univalves of this class observed in the Mohawk River, 

 (except Valvata tricarinata, which is pretty uniformly white.) There are, how- 

 ever, constant features which seem to characterize the species. 



Specimens in which the prevailing tints of the soft parts are salmon or 

 orange, have the anterior margin of the inferior surface of the foot marked 

 with a not very well-defined border of orange, which is darkest where lightest 

 in the preceding species ; back of this, and covering nearly the whole bottom 

 of the foot, is an area of purplish slate color, surrounded entirely by a narrow 

 orange or salmon margin, which is not well-defined, except as limited by the 

 margin of the foot. 



In other specimens of lighter color, no obvious zones appear, the anterior 

 being pale, nearly white, and the translucency of the posterior parts permit- 

 ting a faint reflection of the operculum and shell to be seen through them, 

 presents a darker appearance. In some instances the variety of color is di- 

 versified, and presents a faint purplish slate-colored area of horse-shoe 

 shape within a border of lighter color forming the posterior margin of the 

 foot. 



The superior surface of the foot near the anterior margin is marked with a 

 few black lines, parallel with the margin. Back of the angle of the foot these 

 lines are limited to a narrow zone along the lateral margin of the foot, where 

 they are irregular and inosculate with each other, and frequently terminate 

 downward in the margin of the foot. Approaching the neck, after leaving the 

 lineated margin of the foot, the surface presents a beautiful granulated ap- 

 pearance, from the effect of numerous, minute, brilliant yellowish or orange 

 spots (of a faint greenish tinge), irregularly yet densely distributed over a 

 surface of greenish black. There is no appearance of sinus or fold in the 

 margin of the foot and side of the neck. 



The rostrum is wider and shorter than in the preceding species, and pre- 

 sents a very robust appearance when the two species are compared. The 

 upper surface is marked with numerous well-defined transverse black lines ; 

 between these the prevailing color of the surface is salmon or orange, with a 

 dirty greenish tinge. Usually the end of the rostrum is of a green tint, like 

 that produced by certain salts of copper when combined with organic matter. 

 This color is seen whether the parts are inspected from above, below, or in 

 front. One specimen in which this feature was absent presented all the other 

 prominent characters of the species. 



The tentacles are large at their base, less elongated and not so slender as in 

 the preceding species. At their base they are surrounded by a dense band of 

 brownish black, well-defined towards the head, but fading away indistinctly 

 on the side towards the end of the tentacle. This band is constant, and seems 

 to be characteristic. The tentacles are usually of a beautiful ruddy salmon 

 color, lighter near the tips, where the surface is quite regularly marked with 

 black bands, imparting a jointed appearance to these organs. These bands 



1862.] 



