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CHAPTER XXXIY. 



VARIOUS FORMS OF BULLID^. — SCAPHANDER, OR BULLA LIGNARIA. — 



GRINDSTONE GIZZARD. AKERA. — CYLICHNA. — AMPHISPIRA. TORNA- 



TELLA. — PIIILLINE. — BULLA. 



BULLIDJE. 



The very variable manner in which the lobes of the head 

 and foot are spread out, winged, fingered, or eared, as the 

 case may be, in various genera and species of this interesting 

 family, and the different proportions, shape, and positions 

 of the shells, or even in some genera their absence, show 

 how difficult it is for naturalists to select any characters 

 which can be relied upon, with certainty and consistency, 

 in attempting to arrange objects according to their natural 

 affinities. 



Before my eyes, while writing this, is a plate representing 

 eighteen of the twenty-one genera into which this family is 

 now divided ; and certainly a more seemingly heterogeneous 



