230 INVERTEBRATA OF MASSACHUSETTS. 



Shell minute, conic-globose, thin, translucent, smooth, or with 

 most delicate lines of growth; varying from a bronze-green to a 

 light olive-green color, but usually invested with mud ; whorls 

 four or less, very convex, and flattened near the suture, so as to 

 present a conspicuous shoulder ; the last whorl rather more than 

 two thirds the length of the shell, and as broad as long ; suture 

 deeply impressed, almost channelled ; aperture nearly circular, 

 both lips being about equally curved, and uniting posteriorly at a 

 broad angle ; lips sharp, in some instances a little everted ; inner 

 lip, at maturity, barely touching the preceding whorl just before it 

 joins the outer lip, leaving a very large, deep umbilicus. Length 

 2^ inch, breadth /„ inch, divergence 68"-^. 



Found in ditches and brooks, clinging to stones or submerged 

 plants, oftentimes in great numbers. 



Animal a light drab-color tinted pink, the head a little flesh- 

 colored above ; tentacula silvery, with a dark line running along 

 the outside from the eyes, which are at the external base ; foot 

 not reaching beyond the first whorl, broadly rounded behind, di- 

 lated into angles at each side in front ; head half the width of the 

 foot, and projecting beyond it, motions very slow. In delicate 

 and clean specimens, a dark mark parallel to the outer lip, and 

 another bisecting it, and belonging to the animal, appear through 

 the shell. 



Under this species I include all the small shells, hitherto regarded 

 as PALUDiNiE, which are collected in this region, ascribing the very 

 great differences they present in color and size to differences of lo- 

 cality and age. The shoulder of the whorls, the conspicuous umbil- 

 icus, and the rounded aperture, almost like Valvata or Cyclostoma, 

 are the most obvious characters. It is less solid, less elongated, the 

 aperture more circular, and the inner lip much less closely appressed 

 to the preceding whorl than P. limosa^ Say. P. lusfrica, Say, is de- 

 scribed as much smaller, much more elongated, and more cylindrical. 

 This I strongly suspect to be identical with Valvata jnqjoidea in an 

 immature slate. It approaches nearest to P. Cmcimiaticnsis, Anthony, 

 which is laro;er and more conical and elongated. 



