98 



THE GEOLOGIST. 



Lign. 1. — Cast of Dorsal Valve of Cyrtina septosa. 



a Adductor, or posterior occlusor. 

 a' Adductor, or anterior occlusor. 



Lign. 2. — Magnified Views of Casts of Athyris ambigua. 



Fig. 1. Internal cast of the c?or.s«Z valve. I Fig. 2. Internal cast of valve, 

 a Adductor, or posterior occlusor.* a Adductor, or occlusor. 



a' Adductor, or anterior occlusor. j r Cardinal, or divaricator. 



* In order to avoid further repetitions, I may mention once more that the 

 muscles the function of ^yhich is to open or separate the valves have recently been 

 termed dimricators and accessory divaricators by Mr. Hancock ; and those the 

 function of which is to act in the closing of the valves have been termed anterior 

 and posterior occlusors by the same distinguished zoologist. The divaricators aie 

 those usually termed " cardinal muscles" (" adductor brcvis " of Owen ; " muscles 



