92 Mr Gray on Testaceous Mollusca. 



On this subject I may observe, that I was some time ago in- 

 formed that Area senilis was found in the rivers of Africa in 

 company with Galatea radiata : M. Cailliaud, however, assures 

 me that this is by no means the case, the shells in question being 

 found near the mouths of the rivers, but never in the rivers them- 

 selves. 



One of the most decisive facts regarding the finding of the 

 same species of shell in both salt and fresh water is noticed by 

 Say.* Speaking of Theodoxus reclinatus^ he observes, " I found 

 this species in great plenty, inhabiting St John's River in East 

 Florida, from its mouth to Fort Picolata, a distance of one hun- 

 dred miles, where the water is potable. It seemed to exist equally 

 well where the water was as salt as that of the ocean, and where 

 the intermixture of that condiment could not be detected by the 

 taste." The shell in question is determined by specimens which 

 I received from my late friend himself (to whom science is so 

 deeply indebted, and especially for his researches into the zoology 

 of North America), to be the Neritina Meleagris, obtained in 

 such abundance from the West Indian Islands. Nilsson, too, 

 as before mentioned, has noticed the Neritina Jluviatilis, which 

 in this country is not observed to inhabit ditches in the neigh- 

 bourhood even of brackish water, living on the coasts of the Bal- 

 tic, in brackish situations, in company with LymncBa Balthica 

 and Z. succinea ; and M. Rang found Neritina auriculata in 

 similar situations. 



According to the observations of Olivier, the Ampidlaria ovata 

 inhabits Lake Mareotis, where it is taken in company with ma- 

 rine shells found also in the Mediterranean ; and I have lately 

 received (dead) specimens from the locality indicated. The same 

 species was found by M. Cailliaud in fresh-water lakes in the 

 Oasis of Siwah, where it is called bozue, and eaten as food. It 

 thus appears to be found both in fresh and brackish water. Two 

 of the species referred to this genus by Lamarck, his Ampullaria 

 AveUana and A.Jragilis^ are truly marine ; but they differ from 

 the others in animal and operculum, as well as in the sinuated 

 form of the outer lip of their shell. 



The common cockle of the shops, Cardium edule, is constant- 

 ly to be seen in the ditches of brackish water in the neighbour- 



• Journal of the Academy of Natural Sciences of Philadelphia, vol. ii. p. 258. 



