ANALYTICAL INDEX. 



107 



CHAPTER III— continued. 



Process of evolutions singular, 

 Natural prey of the leech tribe, 

 Plate XI. described. 



PAGE 56 

 ib. 

 ib.' 



CHAPTER III.— BIVALVE SHELLS, 



Form and habits of the bivalve not so easily ascertained. 

 The Si/stema Natura imperfect. 

 Shells an ingredient of traffic. 

 Organic distinctions probable among the bivalves, 

 Genera of both univalves and bivalves numerous, 

 Many of the univalves terrestrial, . . . " 



Some of the bivalve tribe the largest of the Testacea, 

 Their progression slow and laboured. 

 Faculty of forming threads by which to anchor, 

 Glutinous matter lubricates the body, 

 Substance of the byssus various, 

 All the animal secretions extraordinary. 

 Calcareous secretion originates with the embryonic state. 

 Some of the shells very fragile. 

 Structure of shells illustrated by Dr Carpenter, 

 Shell undergoes progressive modification. 

 The size and quality of shell fish dependent on the site. 

 Instincts of the bivalves imperfectly displayed. 

 Enjoy fresh supplies of water, and exhibit a sense of security 

 byssus, ..... 



1. Mytilus — TJie Mussel, .... 



The mussel perhaps the most valuable of the bivalves, 



Mytilus edulis, ..... 



Used as food, ..... 



Some of them deleterious, .... 



Test of boiling them with a silver coin. 



Edible mussel very profusely dispersed. 



Mussel beds sometimes remote from each other, . 



Seed pearls found in the mussel, 



Mytilus pellucidus, .... 

 Shell described, ..... 



Considered a j'ounger stage of the Mytilus edulis. 

 It is comparatively rare, .... 



in the 



57 



ib. 

 58 

 ib. 

 ib. 

 59 

 ib. 

 ib. 

 ib. 

 60 

 ib. 

 ib. 

 61 

 ib. 

 ib. 

 62 

 ib. 

 ib. 

 ib. 



63 



ib. 



ib. 



64 

 ib. 

 ib. 

 ib. 

 ib. 

 65 

 ib. 



ib. 

 ib. 

 ib. 

 ib. 



