REPORT OF THE DIRECTOR I920-2I 169 



So far account has been taken only of the occurrence of marine 

 Pleistocene invertebrate fossils. While it is not intended here to 

 place too great weight upon the occurrence of fresh-water fossils, 

 nevertheless, considering the conditions found in the Baltic, the 

 possible significance of the association of marine and fresh-water 

 forms in Pleistocene deposits should not be overlooked. At 

 Clarenceville, an outport of Missisquoi county, Quebec, between 

 the Richelieu river and Missisquoi bay, four species of fresh-water 

 fossils are found in the deposits with Mya arenaria and 

 Macoma groenlandica. Three of these species, U n i o 

 rectus Lam., Unio cardium? Rafinesque, Unio ven- 

 tricosus Barnes, are represented by large and thick shells better 

 developed than those of the St Lawrence river at present. A 

 species of Limnaea also occurs here (Dawson, 1894, p. 58, 238). 

 A similar occurrence of fresh-water fossils has been noted (Ref. 

 cit.,p. 238, 245, 246, 248) at Pakenham Mills, in Lanark county, 

 about 30 miles southwest of Ottawa, and about 20 miles east of the 

 western limit of known marine fossils (Coleman, p. 130). A 

 Sphaerium? was found here associated with fresh- water 

 bivalves and Macoma groenlandica, but the specimens 

 were too imperfect for certain determination. Other species 

 reported from the Saxicava sand and Leda clay of this locality are : 



Amnicola limosa (Say) Valvata tricarinata Say 



A. porata (Say) Planorbis bicarinata Say 



Limnaea palustris Muller P. trivolvis Say 



L. elodes? Say P. parvus Say 



Patula(Pyramidula) striatella Anthony Campeloma decisum Say 



From the villages of Avonmore and Monklands, south of Ottawa, 

 Coleman (p. 132) reports fresh- water shells of at least eleven species. 

 At Montreal were found two species of Limnaea, L. umbrosa 

 Say and L. caperata Say (Dawson, 1894, p. 245), and from 

 Mallett's Bay, Vt., (Perkins, 1909-10, p. 55) is reported H e 1 i x 

 (Pyramidula) striatella found in the Leda clay. In 

 the Montreal and Vermont areas the fresh-water species very 

 probably were carried in by streams. The occurrence of fresh- 

 water fossils together with Macoma groenlandica and 

 Mya arenaria at Clarenceville is very suggestive of estuarine 

 conditions. The Pakenham Mills area, to which fresh- water fossils 

 are peculiar, is of great interest in this connection. Two of the 

 genera, Planorbis and Limnaea, and one species, 

 Limnaea palustris, which were found adjusted to the 



