LITTORINA. 53 



resembles too closely that of the next species ; and the 

 habitat is constantly different. The animal, moreover, 

 is oviparons. It is possible that occasionally hybrids 

 may be produced between it and rudis, which may ac- 

 count for the rare specimens contained in a few cabinets 

 exhibiting an apparent combination of the characters of 

 both. 



3. LiTTORiNA RUDis. This is the form which has been 

 most divided into so-called species. We believe, with Mr. 

 Jeffreys, that jmtula, tenebrosa and saxatilis, with the 

 many less distinct varieties which we have enumerated 

 under this synonymy will eventually prove to be this 

 species modified by variations in the habitat. The animals 

 of all too nearly resemble each other, and have the common 

 character of being viviparous. Of the more remarkable 

 varieties paiula and sawatilis are rock-inhabiting specimens, 

 the former living mostly on the edge of high- water mark, 

 the latter in crevices near the low-water line, whilst rudis 

 inhabits stones within the half tide belt, and tenebrosa 

 muddy and brackish water localities. They have all a 

 power of maintaining life for a long time out of the water ; 

 this they possess in common with many mollusks exposed 

 to the air at the fall of the tide. Mr. Barlee has observed 

 it in Trochus lineatus, which species he has kept alive 

 away from the sea for as many as eighteen days, whilst 

 ziziphinus rapidly perished, 



4. LiTTORiNA LiTTORALis. Uudcr tliis specics, which in 

 several respects, especially in the features of the animal, 

 approximates the Littorinte to the Lacuna, will probably 

 ^SiW fahalis, and, we feel almost sure, palliata. 



