+78 axel a. olsson 



Explanation of Plate 5 



Figure Page 



Litharca lithodomus (Sowerby) 78 



1-la. Hinge and cardinal area of a left valve at two different degrees of magni- 

 fication. Note the sloping line which begins below the corroded beaks 

 and extends to the hinge line dividing the hinge teeth into two un- 

 equal series. The longer end is anterior. 



lb. The same shell as above, length 104 mm. Manta Ecuador. PRI 25524. 



Ic. Ventral view of a shell with closed valves and shows the narrow, open 

 gap a little in front of middle. Length 86.6 mm. Holotype, British 

 Museum (Nat. History). 



Id. A small left valve which shows some details of its surface sculpture, 

 the umbones worn by abrasion. Small tufts of the periostracum remain 

 along the posterior umbonal angle. Length 45.5 mm. Manta, Ecuador. 

 PRI 25524a. 



le. A much smaller shell showing the higher beaks and wider cardinal area. 

 Length 12.8 mm. Manta, Ecuador. PRI 25524b. 



If. Soft parts of a specimen preserved in formalin, the shell and most of 

 the mantle removed. Left side, aa and pa, anterior and posterior ad- 

 ductor muscles; c, ctenidium; f, foot; by, byssal plug. Length of 

 animal 70.7 mm. Manta, Ecuador. USNM. 



