34 



Animal Life by the Sea-shore. 



attention to the animal than to tlie sheU when, as at the seaside, 

 he is in a position to examine both. Far from deprecating 

 the formation of a collection of shells, we only wish to point 

 out that the interest in these beautiful or curious objects is 

 much enhanced bj' a knowledge of the structure of their tenants. 

 We can gain some idea of them by an inspection of the inner side 

 of an ' mpty bivalve shell, where distinct impressions are left 

 by some of the more characteristic organs of the animal. Scars 

 caused by the insertion of the large muscles which extend from, 

 one valve to the other and close the shell will tell at a glance 

 whether one or two of these organs were present ; if two 

 whether they were equal in size or not, while a narrow line 

 connecting these scars and running nearly parallel with the 

 edge of the valve is the impression left by the muscular border 



pa 



- a. c^ 



FIG. 34. INSIDE OF LEFT VALVES OF CITHERE,\ CHIONE AND 



PECTEN VARIUS ; /;, THE HINGE LIGAMENT ; a a, SCARS OF ADDUCTOR 

 MUSCLE ; p a, POSTERIOR ADDUCTOR ; p i, IMPRESSION OF FOOT ; 

 p. PALLIAL line; S, SINUS OCCUPIED BY RETRACTOR OF SIPHON. 



of the mantle (Fig. 34). This line, termed the pallial hne (from 

 pallium, mantle), if incurved near one of the muscle-scars, 

 reveals the presence of a retractile siphon, and its degree of 

 curvature is an index to the size of this organ in the animal. 



The Scaphopods (the name meaning spade-foot) form the 

 last principal group we have to mention. It is a quite small 

 group, including only the pecuhar Tooth-shells, represented 

 with us by Dentalium elephantimiin, the shell of which is 

 suggestive of an elephant's tusk in form and whiteness, but 

 hollow throughout and open at each end. The animal is slender, 

 and its foot, which may be seen projecting from the wder 

 interior orifice, is conical in shape and provided with two 



