MOLLUSCS, VERMES AND HYDROZOA 



with lines of growth, with the body whorl slightly depressed. The suture 

 is distinct, the apex compressed and the aperture dilated and deflected to 

 the left; the other side showing the whorls nearly as well defined. The 

 body is a dusky brown or russet, and the filiform tentacles are long and 

 marked with dark brown lines. It inhabits streams of colder water in 

 New England, New York, Northern Pennsylvania, Ohio and Illinois, and 

 has been occasionally met with in the vicinity of Philadelphia. 



P. trivohis. Fig. 170, is a very generally distributed species having a 

 laterally flattened ^ to % inch in diameter yellowish-green or brown shell, 

 which consists of four and a half cylindrical whorls with finely marked lines 

 of growth, and is slightly keeled towards the left side. The aperture is 

 also deflected to the left. The spire is slightly impressed, nearly level on 

 the right side, but the left side is considerably depressed and the whorls 



FIG. 1 70. Planorhis trmolvis, four views. Slightly enlarged. 



disappear in a depression about two and a half whorls from the apex. 

 The body is dark brown dotted with ochre and the tentacles long and 

 slender. This snail occurs very generally in the Eastern and Middle 

 States and is found in the Delaware and Schuylkill rivers. Its eggs are 

 laid in a yellowish vermiform mass and hatch in 12 to 20 days. 



P. magnificus. Fig. 171, is the largest recently known American species, 

 having the flattened sinistral shell very large and heavy, about i )4, inch in 

 diameter and i inch high. The upper or spire half of the shell is pale- 

 brown and the lower half dark-brown. The surface is glossy and marked 

 by fine lines of growth. The spire is narrow, the suture depressed, and 

 the summit of the nearly five complete whorls acutely angular and the 

 umbilicus deeply funnel-shaped. The base of the whorls is so narrowly 

 rounded as to appear almost angular. The last whorl is very large, rounded 

 at the periphery, and the irregularly ovate aperture but slightly oblique. 



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