Notes on Freshioafer Mollusca. 243 



starting point. A sraa'l dredge with a handle from fourteen to twenty- 

 feet long, and a boat, arc indispensable, as most of the species are found 

 in deep water. I have often dredged up as many as a thousand shells 

 at a single haul. Some species still live in the Chicago 'river, notwith- 

 standing the immense sewage of the city. The species enumerated in 

 this paper are also common to Lake Michigan. The following is the 

 result of my observations : 



Limncea reflexa, Say — A \qyj abundant shell in all our waters. 

 Lhnmm zebra, Tryon — Abundant in the Calumet and other streams. 

 Without doubt, the same as reflexa; only found in July and August, 

 when L. reflexa changes, under the influence of the atmosphere and a 

 hot sun, from its usual appearance to more brilliant colors. Limncm 

 appressa, Say — This beautiful species i^ very abundant in the Calumet 

 river, and in the lakes" before mentioned. It attains a larger size than 

 any I have seen from other points. L. appressa and L. jugidaris, of 

 Say, have both been referred to L. stagnaUs, Linn. But the first I 

 consider a distinct species. It is always longer and more slender, a 

 character that maintains itself fully in the young shells. L. jugularls 

 more resembled stagnalis, especially in the dilation of the last whorl. 

 Both species may be found in the same localities. Limncea palustris, 

 Muller — A varied slicU .and abundant. Limna caperatcea, Say — 

 Abundant. Lhnmm umbrosus, Say — An abundant shell. AVhether 

 entitled to the name of a distinct species, I will not assume ta say. 

 Of the genus Physa, two species are found in our waters — Physa 

 grjrina, Say, and Fhjsa heterostropha, Say; I have not, as yet, seen 

 any others. The PJiyms. excel all other Limna^idce that I have seen in 

 the quickness of their movements and their tenacity of life. • I have 

 seen them attack bugs Avith the greatest ferocity, and drag them 

 beneath the water. When removed from their native element, they 

 live twenty-four hours or more, and exhaust themselves in the vain 

 effort to reach a more agreeable situation. The following species of 

 PlunorbincR occur plentifully : i^^«. campamdatus, Say ; Pla. irivolvls^ 

 Say — very large; Pla. parvus, Lea.; Pla. hicariaatua, Say. Of 

 Segmentina, we have S. armigera, Say. The genus Valoata is repre- 

 sented by V. tricarinata, Say, in the deeper waters, and V. sincera, 

 Say, in the swamps. The former I dredged from a depth of fourteen 

 to twenty feet. The finest species of univalves we have, is V. contcc- 

 ioiclcs, W. G. B. The shells are found in the Chicago river, but 

 finer and more abundant specimens come from the Calumet and Lake 

 Wolf. Mclantlw suhsoUdm, Antli., are found abundantly. Melantho 

 coarctata, Lea, occurs in the Chicago river. This is probably the 

 exilis, Anth. Of the smaller species, BjOi. ohiusa, Lea, I brought up 



