344 LITTORINID^. 



of a seaweed; and they may sometimes be observed 

 floating in a reversed position^ the sole of the foot being 

 on a level with the surface of the water. The spawn 

 forms a gelatinous but firm cylindrical mass, and is 

 curved in a semicircle. As soon as the fry emerge from 

 their receptacle they swim about freely by means of a 

 ciliated and vibratile bilobed veil, which occupies the 

 front of the body. The otolites are circular and simple. 

 Clark proposed to merge this apparently natural genus 

 in Littorina ; Leach, on the other hand, divided it into 

 Temina, Epheria, and Medoria. The principle of classi- 

 fication advocated by the one was synthetical ; he re- 

 duced genera to species. The other pushed the ana- 

 lytical system to an opposite extreme ; consequently in 

 his hands species became raised to genera. 



1. Lacuna cras'sior"^, Montagu. 



Turho crassior, Mont. Test. Brit. p. 309, t. 20. f. 1. L. crassior, F. & H. 

 iii. p. 67, pi. Ixxii. f. 5, C. 



Body yellowish-white, or pale yellow, with an orange tint 

 on the upper part ; there is sometimes a dark brown triangular 

 spot a little behind the point of the muzzle : mantle thick : head 

 produced into a rather long, narrow, and compressed square- 

 pointed muzzle, having an oval disk in front, which contains 

 the mouth : tentacles slender, tapering gradually to a rather 

 sharp point : eyes black, seated on short tubercles, one at the 

 outer base of each tentacle : foot broader and slightly curved 

 in front, with small lobe-like corners, occasionally sinuated in 

 the middle on one side or the other, and rounded behind ; sole 

 double -edii'ed, apparently sht in three or four places behind : 

 appendages curved and white, very much shorter than the 

 tentacles, which they resemble in shape. 



Shell turreted, bluntly angulated at the base, solid, opaque, 

 lustreless when covered with the epidermis, under which it is 

 somewhat glossy : sculpture, numerous sUght and sinuous spiral 

 impressed lines or wrinkles, which are to a great extent con- 



♦ More solid than other species. 



