196 FRESHWATER FAUNA 



character from the marine lamellibranchs of Devonian 

 age ; and judging by its size, which rivals that of existing 

 Anodonts, appears to have flourished under remarkably 

 favourable circumstances. Somewhat recently, Amalitzky 

 has described the occurrence of another group of fresh- 

 water shells, possibly related to Anodonta, from the 

 Devonian beds of Kussia ; these are the Anthracosiidse, 

 which are also met with in these islands in beds of the 

 Carboniferous system, and under such conditions as 

 suggest their freshwater nature. In deposits of upper 

 Permian age, Amalitzky has also discovered specimens of 

 Palseanodonta, Oligodon, Palteomutela, and several genera 

 of the family Anthracosiidse ; in association with Estheria, 

 Cypris, and remains of plants and reptiles. The world- 

 wide distribution of Unio and Anodon at the present 

 day, and their extraordinary richness in subgenera and 

 species, are in complete harmony with their appearance 

 thus early in the stratified series. 



The freshwater crustacean Estheria is also first met 

 with in the Devonian rocks, Cypris in the Carboniferous. 



No freshwater univalves have yet been recorded from 

 Palaeozoic rocks,* but land shells (Pupa and Conulites) 

 closely allied to Helix, the common garden snail, have 

 been found in the Carboniferous deposits of Nova Scotia 

 (Fig. 68). But the pond snail (Limnaea), the fresh- 

 water limpet (Ancylus), and Planorbis are no very 

 distant relatives of the Helix family, and might, therefore, 

 fairly be looked for in rocks of the same age. We do not 

 actually encounter any of them, however, till the Jurassic 

 period, and Ancylus does not occur before the Miocene, 

 though Acroloxus, a member of the family Ancylidse, is 

 found in the Laramie beds or uppermost Cretaceous of 

 North America. 



* Suess cites Planorbis from the coal measures of Upper Silesia. 

 " Das Antlitz der Erde," vol. ii. p. 303. 



