202 NEW YORK STATE MUSEUM 



but it is however quite clear that the change in local conditions 

 initiating this deposit of estuarine or fresh- water sediments mani- 

 fested itself at a continually earlier period of the Devonic, as 

 one proceeds eastward from central New York toward the Hud- 

 son river. 



The three known occurrences of Amnigenia; A. cats- 

 k i 1 1 e n ,s i s in New York and Pennsylvania, A. j u k e s i in 

 Ireland and (according to Freeh) in Devonshire, and A. 

 rhenana in the Rhineland, are thus alike in the nature of 

 the involving sediment, viz sandstones and sandy shales bearing 

 terrestrial plant remains, but with a total absence of marine 

 organisms; and are essentially equivalent in age, marking only 

 different stages or levels during the continuance of Old Red 

 sedimentation,. 



We have observed that data of this kind are stronger evidence 

 of* the fresh-water habit of this clam than any that can be derived 

 from the structural characters of the fossils themselves in their 

 present preservation. There is however in all a strong Ano- 

 donta or Unio aspect. As the hinge in these genera is 

 normally but slightly diversified, little but negative evidence is 

 to be expected from the fossils. The absence of hinge structures 

 in all these cases is such evidence of much weight wherein we 

 may find indication of close conformity in structure. Bens- 

 hausen is disposed to caution in inferring-, in the absence of 

 more positive indications, immediate relationship to Unio or 

 Anodonta, and concludes that, " though Amnigenia may be 

 regarded as the forerunner of the recent Unios, one will 

 do well not to infer a direct phylogenetic connection by the 

 employment of the term Anodonta, for which all proof fails" 

 (p. 8). We figure here a slab of Oneonta sandstone from 

 the Clarke quarry at Oxford, which bears 3'0 shells of A. cats- 

 ki 1 1 e n s is on a surface 14 by 10 inches. Some of these shells 

 have apparently been drifted into their places, but several pre- 

 sent the appearance and attitude of shells which had been boring 

 in the mud. The valves are all double and closed, so that they 

 must have been buried fast in the sediment while alive or before 



