100 . III. DIST. CHAR. Prototype. 



ft. ) 76. Cortical (corticate) having its origin from 

 the outer lark. 



at the margin. The indentations in the margin of the sinus 

 are to be numbered by the points, which are directed to- 

 wards the beak of the smaller valve. They vary from two 

 to nine : when they exceed that number, the sinus is properly 

 said to be dentate, crenate, &c. The plaits or waves of the 

 margin are not always continued by the same kind of folds 

 down the ridge and channel those of an angular form fre- 

 quently passing into obtuse or rounded furrows, while the 

 waved are often continued by sharp-ridged folds. In many 

 instances, also, the indentations at the margin of the sinus are 

 very large and strong, without any correspondent folds on the 

 surface of the valves. 



Dentate (dentatus) with small indentations in the margin. 

 * * Ridge and channel. 



,) Continued (continuatus) when the bending at the margin is 

 continued down the valves by the ridge and channel, w r hich 

 gradually diminish till they reach the beaks. 



Half-continued (semi-continuatus) continued by the channel 

 down the larger valve ; but without the correspondent ridge 

 in the other valve. 



Abbreviated (abbreviates) not continued down to the beaks 



growing obsolete at a small distance from the margin. 

 /A) Striated (striatus) with the ridge and channel longitudinally 

 marked with slender lines. 



Sulcated (sulcatus) with the ridge and channel longitudinally 

 marked with deep and broad lines. 



Smooth (I avis) neither striated nor sulcated. The ridge and 

 channel of the sinus are often smooth, when the lateral parts 

 of the valves are marked or scored with lines. 



