10.— Plate I. 



strongly spine-tubercled at the periphery ; columella 

 shortly twisted, appressed, canal broadly effused. 

 Anthony, MS., in Mus. Cuming. 

 Hab. Tennessee, United States. 



This and I. spirostoma are probably varieties of the same 

 species. In one the channelled extension of the aperture 

 and columella is broadly flatly effused, in the other it is 

 twisted over into a spiral. 



Species 5. (Mus. Cuming.) 



Io fluviatilis. Io testa pyramidali-fiisiformi, solidis- 

 simd, virescente-olivaced, purpureo tinctd, anfractibus 

 sex, plano-declivibus, ad peripheriam acute augulato- 

 cariuatis, obtuse tuberculoid, tuberculis distantibus, 

 fere obsoletis ; columella sube.longatd, parum contortd. 



The river Io. Shell pyramidally fusiform, very solid, 

 greenish-olive, purple-stained, whorls six, flatly slo- 

 ping, sharply angularly keeled at the periphery, 

 bluntly tubercled, tubercles distant, almost obsolete ; 

 columella rather elongated, but little twisted. 



Fusus fluviatilis, Say. 

 Io fluviatilis, Lea. 



Hab. Tennessee, United States. 



Of a straighter fusiform growth than the other species 

 of this type, with the whorls sloping])' compressed into a 

 keeled angle. There are indications of tubercles at the 

 periphery, but at very irregular intervals. 



Species 6. (Mus. Cuming.) 



Io FUSiroRMls. Io testa fusiformi, virescente-olivaced, 

 purpureo fasciatd, anfractibus sex, concavo-declivibus, 



ad peripheriam tumidis et irregulariter plicato-nodu- 

 latis, uodis plus minus obsoletis ; columella teuuiter 

 elongaid, subcoutortd. 



The fusiform Io. Shell fusiform, greenish-olive, purple- 

 banded, whorls six, concavely sloping, swollen and 

 irregularly plicately noduled at the periphery, nodules 

 more or less obsolete ; columella thinly elongated, 

 slightly twisted. 



Lea, Trans. Amer. Phil. Soc. vol. iv. pi. 15. f. 37. 



Hab. Tennessee, United States. 



Characterized by the same swollen gouty appearance 



and by the same bent manner of convolution as I. tene- 



brosa ; indeed, I am unable to detect any specific difference 



in it. 



Species 7. (Mus. Cuming.) 



Io spinosa. Io testa symmetric}, fusiformi, flavescente- 

 olivaced, pal/ide purpureo-fasciatd, anfractibus sex, 

 concavo-declivibus, ad peripheriam prominente oblique 

 spinoso-tuberculatis ; columella productd, eleganter cou- 

 tortd. 



The spined Io. Shell symmetrically fusiform, yellowish- 

 olive, faintly purple-banded, whorls six, concavely 

 sloping, prominently obliquely spine-tubercled at the 

 periphery ; columella produced, elegantly twisted. 



Lea, Trans. American Phil. Soc. vol. v. pi. 19. f. 79. 

 Io biennis, Anthony. 



Hab. Tennessee, Virginia, United States. 



The type of the genus in its most symmetrical form of 

 development, from which /. spirostoma and brevis are 

 clumsy departures in what Mr. Darwin terms the " struggle 

 for life." 



