Cowry and Pyramid-shells 247 



flat for crawling, as in those that crawl upon rocks 

 or weeds, is developed into fin - like expansions. 

 With these they swim in an inverted position at the 

 surface. The shell is not present, or is very small, in 

 one family (Pfero^?'acA a^iWa^); in another {Atlantidoi) 

 it is spiral, and sufficient to entirely accommodate 

 the animal, which shuts itself in with an operculum. 

 Both shell and animal are perfectly translucent, so 

 that the internal organisation is clear without 

 dissection. These creatures had not been regarded 

 as coming within the British area, though they 

 swarm in the warmer parts of the Atlantic, as 

 well as in the Indian and Pacific Oceans ; but in 

 September 1888 Professor M'Intosh took in the waters 

 of St. Andrews Bay " a small transparent univalve, 

 like a finely fashioned shell of glass, containing its 

 inhabitant." It measured about one-twelfth of an 

 inch, and w^as probably a young example. It was 

 evidently a species of Atlanta, nearly allied to that 

 figured, but having a flat margin instead of the keel 

 that is present in Atlanta j^eroni. Such a capture 

 is of great interest, for hitherto these creatures were 

 considered to exist only in more genial seas. 



