Egijpfian MoUusca 101 



Flanorhis mareoticus, Innes, 1884. 

 This small Planorhis is very common in the ponds at the Zoo- 

 logical Gardens and elsewhere in Giza. Specimens were frequently 

 found at Marg. 



«^' 



Fig. G4. — Planorhis mareoticus. (x 1\.) 



Pallary says that it is found at Damanhour, Nefische, near 

 Ismailia, and is very common around A.lexandria. 



Ancey is of opinion that this form is the same as P. ehrenhergi. 



P. mareoticus is the intermediate host of a cercaria believed 

 to be the infective stage of a species of bilharzid worm occurring 

 in aquatic birds. 



Egg Deposition in Planorbid^. 

 Among the fresh-water molluscs at Marg we noticed two types 

 of reproduction. There were certain forms like Vivipara and 

 Melania in which the eggs were retained until development had 

 taken place to such a degree that the progeny were provided with a 

 shell showing already characters of the adult. 



Fig. G5.— An egg-mass of Bullinus sp. deposited on weed. 



In other forms, such as Bullinus and Planorbis, the eggs were 

 found depositeil in flat jelly-like masses on weed from the bottom 

 and sides of the stream. Not infrequently similar gelatinous 

 masses were found on the shells of Planorbis and Bullinus. That 

 these were deposited by the individual actually inhabiting the shell 

 seemed little probable. 



