i8 Calvin Goodrich 



Ajiciilosa forciiiani Lea 

 Fig- 4. 5 

 Anculosa forcmani Lea, Proc. Aiiicr. Phil. Soc, ii, p. 243, Dec. 1842. 



In shell characters this species is closer to A. picta Con. than is A. for- 

 viosa Lea. But while the operculum of picta and fonnosa are much alike, 

 that of forcmani is like the operculum of neither. The similarity of the 

 shells of for)iwsa and forcmani, picta out of consideration, varies strange- 

 ly with locality, the resemblances and differences seeming to play a game of 

 see-saw as the collector travels down the Coosa River. At Three Island 

 Shoals, for example, forcmani is a smaller, smoother mollusk than formosa, 

 without the basal band so oddly persistent in that species. At Fort William 

 Shoals the two forms come so closely together that, lacking the opercula for 

 guidance, a large series is required to make identification certain. At We- 

 duska Shoals, the diflferences become more distinct again, foremani retain- 

 ing folds, fonnosa having lost them, the fine lines of color of one being 

 faint, those of the other strong. Thus with each locality there are variations 

 permitting separation of the two species, yet not always because of the same 

 characters. In general, formosa is a larger species, more shining, with 

 slightly heavier columella and a greater tendency as it proceeds downstream 

 to substitute a few bands of color for the many fine lines. If the hypothe- 

 sis is correct that the animal, protected and less subject to environment- 

 al forces, is less inclined to change than the exposed shell of the mollusk 

 then, with the opercula in mind, we may suppose that forcmani sprang from 

 a form distinct from the ancestral forms of picta and formosa. We must 

 explain the marked resemblances of the shell as a g^ise of convergent de- 

 velopment. 



The sculpture of forcmani consists of fine growth lines, microscopic 

 revolving striae being rather rare. About half of the specimens of any 

 given lot have broad, flat folds, more or less distinct and about the same 

 number have nodules at the shoulder which may be termed plicae. 



The fine lines of color are usually interrupted and at places there are 

 shells which, like formosa, acquire a band at the base in addition, though 

 usually this character is not as strongly marked, when it exists, as in the 

 other species. Bands first appear in material from Fort \\'illiam Shoals, 

 the arrangement being four bands with a fine line of color between two 

 of them. Such specimens are comparatively rare and among foremani are 

 noted only from the locality given, Peckerwood Shoals and Butting Ram 

 Shoals. Shells having the pathological character of flammata and ::chra are 

 not uncommon to this species. 



The color of the columella varies from white to red and purple. The 

 collections from Three Islands Shoals have the columella white in four 

 shells in six ; at liutting l\am Shoals, virtually the southernmost point of 

 distribution, purple columellae were to the white in about the same pro- 

 portion. 



The operculum is reddish brown with the edges transparent. It is nearly 

 triangular in most instances and very small in proportion to the size of the 



