Anatomy and Physiology of Anodonta Fluviatilis. 173 



though of frequent occurrence, is always small, seldom or never exceed- 

 ing three inches in length, thin and much eroded. All the species 

 occurring at this locality, with the exception of A. fluviatilis, viz., A. 

 imylicata, U. complanatus, U. radiatus, U. ochraceous, U. cariosus 

 and U. nasutus occur in much better condition than in any other 

 locality in this part of the State. In a pond situated less than a mile 

 from this locality, A. fluviatilis is found of unusually large size and 

 but slightly eroded ; specimens five inches in length, with a height 

 of three inches and a diameter of two and one-half inches are abundant, 

 and some are found measuring more than six inches in length and 

 three and one-half inches in height, as large and perfectly preserved 

 specimens as occur in any locality, while with the exception of this 

 species there is not another shell, in the pond, either bivalve or 

 univalve. In another locality a mile below Albany where Sphterium 

 rhomboid eum is found in abundance and of unusually large size, 

 Anodonta fluviatilis, though of frequent occurrence, is very small ; 

 the largest specimen I have seen, among a collection numbering many 

 hundreds, measures two inches in length. 



A. fluviatilis thrives best in ponds, but is found in quite rapid 

 streams, though even then the most favorable localities are in the 

 comparatively quiet portion of the stream. 



The largest specimens I have seen, were found in the pond mentioned 

 above, near the mouth of a sewer, where the mud was of a slimy char- 

 acter and offensive to the smell. It is claimed that the male and 

 female may be distinguished by the comparative diameter and gen- 

 eral shape of the shell, but I have not been able to so distinguish 

 them. In the fall of 1879 I collected about one hundred and fifty 

 specimens of varying size — the shells were of different shapes and 

 proportions, some quite flat, others extremely gibbous, the diameter 

 sometimes being greater than the height. Among the first sixty I 

 opened, there was not a single male, the outer gills of each specimen 

 being filled with young. The remaining specimens were placed in a 

 tank, and for several months undisturbed ; when I removed these ani- 

 mals from the shells I found only four individuals without young in 

 the outer gills, and as some of the animals had extruded a portion of 

 the young from the gills, it is possible that the individuals above men- 

 tioned may have had the young in the gill pouches earlier r in the sea 

 son but had extruded them all. Though I am not prepared to say 

 that the sexes are not distinct, the fact that nearly every specimen 

 had young in the gills would seem to indicate that condition. 

 When my attention was first called to it, it was too late to make any 

 farther collections that season. The growth of an animal during a 

 year, I have not been able to determine ; an individual which I have 



