LAND AND FRESHWATER MOLLUSCA. 329 



there was a great mortality of this (?) species, occasioned by 

 drought, and by rats devouring them ; the banks of the Cherwell 

 were lined with their shells. Mr. Whiteaves seems, however, to 

 have confused the present species with pictorum, and all his notices 

 under "tumidus" apply with equal force to the species pictorum, 

 which is the commoner of the two forms. Unio pictorum is not 

 mentioned in the list, though it appears in the collection in the 

 University Museum. 



U. pictorum, Linn. — Very abundant, in the Isis and Cherwell, 

 and their communicating streams ; also in the canal. 



Var. latior. — Abundant in the canal. 



Anodonta cygnea, Linn. — Plentiful in all the larger pieces of 

 water, the finest forms coming from stagnant lakes. From 

 Mr. Whiteaves' list I cite the following varieties, though not now 

 to be found in the collection: — 



" Var. rostrata. — In river. 



" Var. cellensis. — In lake at Wolvercot. 



" Var. intermedia. — Lake near South Hincksey." 



A. anatina, Linn. — Plentiful. Mr. Whiteaves considers it 

 commoner than the preceding. 



Fam. III. Dreissenhxe. 



Dreissena polymorpha, Pallas. — Plentiful in the canal, espe- 

 cially about the locks. 



Order Pectinibranchiata. 

 Fam. I. Nerittdje. 



Neritina fluviatilis, Linn. — Rather plentiful in parts of the Isis 

 ami confluent streams, where the bottom is stony and gravelly. 



Fam. II. Paludinidje. 



Paludina contecta, Millet. — Very abundant in ditches around 

 Oxford. Found with the next species, and like it always covered 

 with confervoid growth. 



P. vivipara, Linn. — Not so abundant as the preceding. I have 

 taken it in the Isis near the " Gut," in the Cherwell, and in the 

 canal. 



Bythinia tentaculata, Linn. — Very abundant ; specimens from 

 the canal are smaller, more fragile, and of a pale horn-colour. 



2 a 



