16 RESEARCHES UPON THE HYDROBIIX.E 



not agree with that given by Mr. Haldeman, in his Monograph/ 

 except in regard to the isolation of the egg. This author states 

 that the ova are deposited " in small oblong detached glairy 

 masses, each of which contains apparently but one germ. The 

 color of the germ is orange, of the mass yellowish transparent, 

 with a dark central line upon the surface from end to end." If it 

 were true that the eggs occur in " glairy masses" they would 

 approximate in character to those of the fresh-water Pulmonates. 

 In view, therefore, of the discrepancy between my own observa- 

 tions and those of Mr, Haldeman on this point, it will be proper 

 to state that I have not actually witnessed the deposition of the 

 egg by the mother. I have, nevertheless, no doubt whatever 

 that the eggs which I have described above are really those of 

 Amnicola porata. As far as has yet been observed, the eggs 

 of all the allied Ctenobranchiates are contained in ova-capiules 

 when deposited, and it would be very remarkable if those of the 

 Amnicola formed the only exception. The " dark central line" 

 mentioned by Haldeman probably corresponds to the lamina of 

 the ova-capsule, described above. 



The true Amnicolse are exclusively aquatic, living in the deeper 

 fresh-water lakes, and streams which do not dry up in summer. 

 They creep with a regular gliding motion, the right and left s^ides 

 of the sole of the foot being alternately put forward, as is usual 

 in the creeping rostrifers 



Not having had an opportunity of examining all of the species 

 which have been referred to Amnicola, I cannot, of course, say 

 with certainty how many and what species truly belong to the 

 restricted genus. There is a shining horn-colored shell found in 

 Vermont and New York — which is i^robably the A pa//iV/a of 

 Haldeman, although I have seen it labelled both A. lustrica and 

 A grana — the pupoid form of which, in connection with the shape 

 of the aperture, has led me to suppose it generically distinct. I 

 have, however, recently examined the lingual dentition of this 

 species, and find it to be neai'ly like that of Amnicola po7'nf.a, 

 the rhachidian tooth being exactly similar. The species probably 

 belonging here are, besides Say's Paludina porata and P. limosa, 

 his P. grana ; the Amnicola, orbicidata and A parva of Lea ; the 

 A. decisa, A. galbana, and 4- pallida of Haldeman, and the 



' Monograph of the genus Amnicola, p. 4. 



