The Genus Gyrotoma 27 



smooth, or slightly thickened onlj^ at the fissure; body-whorl striate and banded; 

 /vhorls of the spire not banded, but having a thickened, cord-like line near the suture. 



Habitat : Coosa River. Alabama. 



Length, eleven-sixteenths ; breadth, seven-sixteenths of an inch. Length of aper- 

 ture, seven-sixteenths ; breadth of aperture, four-sixteenths of an inch. — Anthony-. 



This species is close to the form of incisum which has a comparatively 

 deep fissure, as at Weduska Shoals. But the young of that form have the 

 typically shallow fissure. It is not so in the case of amplmn. Moreover, 

 the fissure in ampliim is sometimes straight, never in incisum. Sometimes 

 the lower edge of the fissure of amplum is waved, but this has not been 

 observed in incisum. The depth of the slit in the species under consider- 

 ation varies in adults from 6>^ to 9 mm. The girdle is stout, often ir- 

 regular. 



In form the shell is somewhat cylindrical, noticeably shouldered and 

 in instances slightly constricted though not so frequently or so deeply as 

 in incisum. Ordinarily the mollusk is without revolving folds, but occas- 

 ionally they do occur. Commonly the body whorl bears low nodules just 

 below the suture. Growth lines are fine, often prominent and are crossed in 

 places by waving transverse lines usually discontinuous. The largest speci- 

 men taken by Mr. Smith measures 233/2 x 14^ mm. Color varies from 

 olive-yellow to Mars-brown. The prevailing banding formula is three bands 

 equidistant and of the same width. Bands in this species show a marked 

 tendency to become obsolete. The columella is white to bluish-white, hav- 

 ing a porcelainous node at the fissure and ending at the base in a distinct 

 sinus. 



Anthony erected several species at the same time from shells which seem 

 to have come from Dr. Schowalter just after that collector's first visit to 

 Fort William Shoals. The'ir novelty led to the placing of undue emphasis 

 upon characters of no great significance. Thus recta was made a species 

 principally upon the form of the shell and the absence of bands. The ac- 

 centuation of rest scars was the justification of salebrosa. Robiista was 

 differentiated from salebrosa by reason of its smoothness. Demissa, a sin- 

 gle specimen, appears to have been one of the not -very common adults of 

 the genus which have a fully developed columella. Dr. Lea pubhshed his 

 descriptions of harUnanii and glandula hardly three months after Anthony's 

 names had been printed. His hartmanii is an old, worn and broken speci- 

 men of amplum. It is somewhat difficult to distinguish glandula from in- 

 cisum, but I was enabled to do this with care by means of a photograph 

 sent to me by Mr. W. B. Marshall of the United States National Museum. 

 Showalteriana is a pathological individual. The synonymy of amphim is 

 an illustration of a curious competition in species-naming which obtained 

 among American naturalists in the first half of the nineteenth century. 



Hinkley (2, p. 40) , who found this to be the most plentiful Gyrotoma on 

 Fort William Shoals, identified it as constrictum, apparently following Try- 

 on's decision in the case of recta. I have seen both the type of constrictum 

 and some of Hinkley's shells and can say confidently they are not the same. 



The range of the species is Three-Island Shoals to Peckerwood Shoals. 



