lymn^eim: of north America. 389 



globose form described as L. pinguis by Say, and seems, in many 

 cases, to run very close to that of L. ampla Migh. The Pine Lake 

 examples have usually a very thick, solid opaque shell, and a large 

 proportion are more or less distorted, the most common effect of their 

 unfavorable environment being apparently to induce a very abrupt 

 and rapid expansion of the outer lip, which, in most cases, is ac- 

 companied by a heavy callus deposit all around the aperture." 



The thick opaque texture is characteristic of many of the species 

 from the northern part of the lower peninsula of Michigan. 



Remarks : Catascopium is frequently confounded with palustris 

 and emarginata. It differs from the latter in the manner in which the 

 inner lip is oppressed to the axis, and in having generally a narrower, 

 more fusiform shell and a more elongated aperture. Emarginata is 

 typically umbilicated and the inner lip is widened out to form a broad 

 expansion, quite different from the narrow inner lip of typical cat- 

 ascopium. It differs from palustris in its shorter, wider and less acute 

 spire, in having one whorl less and in" having generally a zvider, more 

 fusiform shell and finer sculpture. The columellar plait is not gen- 

 erally as pronounced in catascopium as it is in typical palustris. Cat- 

 ascopium is, also, seldom malleated while palustris is frequently so 

 marked. The more fusiform shape, zvider shell, one less whorl and 

 the less acute spire will serve to distinguish the majority of specimens 

 of catascopium from palustris. It generally has a thicker shell than 

 that of palustris. 



Dr. James Lewis 1 has advanced some suggestive theories in re- 

 gard to the relationship of catascopium to elodes ( = palustris). Dr. 

 Lewis believed that "An equitable temperature, a moderate supply of 

 food, limited supply of air, and frequent disturbances of the station 

 of the animal by currents in the water, determines the form we call 

 catascopium" while "a warmer station, abundance of food, unlimited 

 access to the atmosphere, and quite stagnant water, favor the develop- 

 ment called elodes." While this statement is true to a certain extent 

 as regards the habitat of the two species, yet the writer has seen no 

 evidences bearing out the theory advanced by Dr. Lewis that the eggs 

 of catascopium will produce palustris when transferred to a different 

 environment. The shell may be (and does) become somewhat 

 elongated and simulate the palustris form, but it is still catascopium, 

 as may be proven by examining the teeth and genitalia. The nearest 

 approach seen by the author of catascopium to palustris is in a lot 

 of shells from the north end of Owasco Lake, Cayuga Co., New York. 



1 Amer. Journ. Sci., IV, p. 4; VI, p. 85. 



