The Genus Gyrotoma 5 



Coosa at Fort William Shoals, Wilsonville and Wetumpka. He distributed 

 a great number of specimens, many of which I have had the opportunity 

 to examine. 



Hannibal (2, p. 179) recognized Gyrotoma as a genus and set down 

 Goniobasis as a subgenus. Under the name Gyrotoma olivida excisa (Lea) 

 he threw together all the forms that are mentioned in Tryon as being deep- 

 fissured, eighteen species in all. Twenty-two, described as having short or 

 shallow fissures, suffered telescoping under the designation Gyrotoma laeta 

 incisa (Lea). Mr. Hannibal was bold, but not without a few misgivings. 

 Preparatory to a prodigious scrambling of the Pleuroceridae he wrote, "It 

 is not anticipated that this treatment will meet with general approval 

 in every instance." 



The Alabama Museum collection of Gyrotomae is, of course, unparalleled. 

 It contains thousands of specimens carefully labelled and so painstakingly 

 cleaned that color and sculpture can be made out quickly and with certainty. 

 Notes by Mr. Smith upon his labels and observations he made in his cor- 

 respondence with Dr. Walker have been invaluable in this study. 



The Environment 



The genus is confined to the Coosa River. It has not been found even 

 within the mouths of creeks flowing into the river. The nature of the 

 liabitat supplies the explanation. Mr. Smith repeatedly wrote of Gyrotomae 

 as living in rapid heavy currents. Speaking of the genus at Wetumpka he 

 said that it was "almost confined to swift water, and those specimens in pools 

 do not look healthy and are apt to be deformed." A permanent habitat 

 of this kind is rarer among Pleuroceridae than is generally supposed. lo 

 and Anculosa do occupy the swifter parts of rivers, the old as well as the 

 young, but most species of Pleurocera are to be found in quiet water. 

 Pleurocera unciale (Hald.), a characteristic east Tennessee species, is in 

 the main part of streams only while partly grown. The adults seek the pools 

 and banks. I have noticed the same thing of Goniobasis livescens (Menke) 

 in Ohio, Michigan and Indiana. Colonies of livescens are found upon 

 wave-beaten rocks in Lake Erie, but far larger colonies inhabit places much 

 more protected. The ordinary bulbous form of livescens lives plentifully in 

 rapids of the upper Wabash River. A depauperate form of the species 

 was collected by Hinkley under stones in the lower part of the river. Such 

 a site, corresponding to that in which Gyrotoma flourishes, was an unhealthy 

 one for a species probably the most adaptive of all Goniobases. 



Distribution 



Gyrotoma first appears in the Coosa at Lock 2. St. Clair County. The 

 only species there and about as far down as the mouth of Yellowleaf Creek 

 of Shelby County is pyramidatum. In the short distance between this point 

 and the foot of Peckerwood Shoals, Talladega County, occur five species 

 which are confined to these reaches, namely, amplunt, cariniferuniy spillmanii, 

 Iczvisii and hendersoni. The second and the last of these five are known 

 from Fort William Shoals only. Alahamensis is first met with sparingly 



