« 20 A Guide to the Zoological Collections in the 



distributed, and in habit and manner of life resemble the 

 true Limpets. 



14th Family, Capulidse [Cases 142A, B]. 



The Capulid% are known as " Cup and Saucer Limpets". 

 They also resemble the true Limpets both in habit and 

 in form, but differ from them in having a single true 

 gill-plume, well developed and on the right side of 

 the neck, as among the Acmceidae. The shell differs 

 from the simple cap-like form of the Limpet and False 

 Limpet in having either the aperture partly covered in 

 behind {e.g^ Crepidula), or the dome furnished with a 

 more or less complete shelly cup (the rudiment of a 

 columella) for the special protection of the viscera [e.g-i 

 Crucibulum). 



15th Family, Littorlnidse [Cases 143 A — 145B]. 



The Periwinkles form a very large and very widely 

 distributed family of herbivorous gastropods, the great 

 majority of the species of which are marine and littoral, 

 often living above high-water mark. The shells are 

 turbinate with the lip smooth and unnotched : in some 

 species they resemble Trochus shells, from which, however, 

 they may be distinguished by the dull (non-nacreous) 

 interior, — the shells of the Trochidx being always bril- 

 liantly pearly (nacreous) within. 



Hydrobia and its alliance, and Assiminea and its 

 alliance, live in brackish and fresh waters, some species of 

 these genera, like the true Periwinkles, being amphibious. 

 The shells of the Littorinidx are closed by a horny oper- 

 culum. 



i6th Family, Paludinid36 [Cases 145C— 147A]. 



The "River Snails" resemble the Periwinkles. They 

 inhabit rivers, lakes, ponds, and marshes throughout the 

 northern hemisphere. They are viviparous. The shells, 

 which generally have the spire produced, are thin, are 



