Anculosau of the: x*\labama River Drainage ii 



those of the preceding group, and doubtless the affinities between the two 

 groups is in general quite close. They have the closely-coiled inner whorls 

 of the taeniata assemblage, are ovate to elongate, dark as a rule. In seek- 

 ing an operculum of ampla to illustrate, none could be found among the 

 river specimens which had any remaining traces of the spiral lines. The 

 figure pictured is the operculum of a creek shell. Damaged and distorted 

 opercula are the rule in this group. The ampla operculum is usually nar- 

 rower in proportion to altitude than others of the group. In miinica the 

 broad operculum illustrated is not wholly characteristic, elongate forms also 

 appearing. The opercula of plicata are in general ovate, the growth lines 

 frequent and strongly-marked. Those of siiiithi are closely related to the 

 opercula of plicata. 



No common characteristic is observable among the opercula of the 

 shozvalterii group. Showalterii itself has a distinctive operculum, elliptical, 

 dark, the margins of adult specimens thickened. The striking feature of 

 the operculum of sulcata is the loosely-coiled spiral lines. Neither of these 

 opercula does the operculum of lirata resemble, though in a longer series 

 than has been at hand the connection might be made more clear. The oper- 

 culum of occultata is like that of a small sulcata. 



The opercula of the com pacta group are small, thin, wath tightly-coiled 

 spiral lines when they appear at all. The organ to a large extent seems de- 

 generate. The operculum of compacta which is illustrated has four whorls. 

 This is probably an abnormality. The fan-like development of melanoides 

 is characteristic also of the operculum of vittata. 



The operculum of ligata is described in detail later on. There exists no 

 close affinity to this form among the other Anculosae, nor is any relation- 

 ship traceable to any kind of operculum so far discovered outside of the 

 genus. 



Ceassificatign 



The Anculosae of the Alabama drainage divide into six groups, four 

 of them well defined, two others which are not so distinctive and might 

 prove upon more thorough study, particularly of the anatomy, to belong 

 to one of the groups whose border lines are of satisfying clearness. 



The picta group consists of six members, characterized by a similarity 

 of shell structure and, to some extent, of opercula. Taking picta as the 

 head of the group, not because it appears to be the most primitive form, 

 but because it is the oldest in point of christening, clipcata and formosa 

 are seen then to be the nearest relatives, with for(*mani more distantly con- 

 nected and in shell characters allied to fonnosa. Dozvniei can be fancied 

 upon this family tree as the direct descendant of formosa, and modcsta as 

 the poor relation of dozvniei. 



For a second gvou\),tacniata has been taken as the leading term. Ths 

 small and not very firmly established local race td{rrefacta is closely 

 allied. Somewhat more distant is coosacusis, another local race, but which 

 yet has acquired an unmistakable individuality and such prosperity as is 

 indicated by large numbers. Griffithiana follows as a seemingly ancient 

 offshoot. Choccoloccoensis would appear to be the descendant of taeniata, 

 or of one of taeniata's antecedents, which invaded a tributary of the main 



