72 CLASSIFICATION. 



grains of sand, may reveal to the naturalist much of 

 the history of the shell of which it is the debris* The 

 importance of such a fact to the geologist is obvious, 

 but I speak of it here chiefly as affording an instance 

 of the wonderful skill with which these humble works 

 of an unseen Worker are constructed. " Lo, these are 

 parts of His ways ; but how little a portion is heard 

 of Him!"t 



In the scientific classification, or the division into 

 genera, of bivalve shells, the most important characters 

 derivable from the shell are to be found in the modifica- 

 tions of the teeth and ligaments of the hinge, the po- 

 sition of the impressions of the adductor muscle, and 

 of the line which marks the adherence of the mantle 

 with the shell. The first of these characters forms the 

 basis of the Linnsean genera. In the simpler forms of 

 hinge, as in the Oyster, the Scallop, and the Mussel, 

 there are no teeth, the hinge consisting of a ligament, 

 either sunk into a triangular pit, or forming a marginal 

 line extending along the shell. The first step in ad- 

 vance of this structure is found in the Mya, or Gaper, 

 where a single spoon-shaped tooth receives the liga- 

 ment. From this upward, through Lutraria, Ifactra, 

 Cardium, &c., we are conducted to exceedingly com- 

 plicated dental processes ; till we find \n-Arca and its 

 allies an infinity of sharp teeth, like those of a pair 

 of combs, fitting accurately into each other. In most 

 genera the number and position of the teeth are nearly 

 the same in all the species. But in a very natural 



* See Dr. Carpenter's paper on this subject in Report of British 

 Association, 1847. f Job xxvi. 14. 



