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Dr. Gould exhibited several specimens of Lymnsea from 

 Lake Superior. 



The distinctions of species in this genus, he said, are very 

 slio-ht and difficult to make out. He, however, was satisfied 

 from a careful examination of the specimens before the Society, 

 that the three species of Say, L. catascopiiim, L. eniarginata, and 

 L. pinguis, are in reality but one. 



Dr. Gould, also, exhibited specimens of Helix liortensis from 

 a small island near Cape Ann. This species, he remarked, is 

 one of the few land shells which have been introduced into 

 America from Europe. Like the same and other species in 

 Europe, it is extremely prolific, and the island from which the 

 specimens were obtained is covered with them. The true Amer- 

 ican species of this genus, on the other hand, produce very few 

 ofispring, and are comparatively very rare. Helix hortensis, 

 as is well known, exhibits very great varieties of marking. The 

 specimens found on one of the islands near Cape Ann are all of 

 the plain variety. On another island, about a mile from this, 

 the banded variety exists in great numbers, the banding in all 

 being precisely the same. It would thus appear that varieties 

 perpetuate themselves. 



Prof. Agassiz remarked, that in Europe very different varie- 

 ties are found in close proximity to each other, as for instance in 

 two adjoining gardens. 



Mr. Ayres exhibited to the Society a new species of fish 

 of the genus Polypierus, from West Africa, recently pre- 

 sented by Dr. Perkins. 



This fish belongs to one of the fossil types, of which several 

 instances exist in America, and of which two have been before 

 described as coming from Africa. It is characterized by the 

 number of finlets on the back, of which in the specimen exhib- 

 ited there are six, commencing very nearly at half the distance 

 from the head and extending to the tail. The throat is covered 

 with hard, bony plates like the scales on the body, which are 

 nearly immovable. This would greatly embarrass the respira- 

 tion of the fish, were it not for two openings on the top of the 

 head, which act as safety-valves, allowing the water to flow 

 through them. The specimen exhibited resembles the fossil 

 types also in the unequal size of the lobes of the tail ; an unu- 



