SPIRIFER. 



have been an opening for the passage of a byssus, by 

 which probably the animal affixed itself to rocks, stones, 

 &c. when living. Two spiral appendages are attached 

 near the umbo within the smaller valve, whose convolu- 

 tions diminish as they approach the smaller points of the 

 shell, (one on each side) most distant from the umbones. 



There are many species, which abound in the Moun- 

 tain Limestone and which are mostly covered externally 

 with striae, ribs or grooves, radiating from the umbones 

 to the ventral margins. 



