1879.] NATURAL SCIENCES OF PHILADELPHIA. 215 



numerous, less prominent on the middle of the whorls; aperture 

 ovate, produced into a short canal. 



Length \ inch. 



Claiborne, Ala. 



This species closely resembles, but is less slender, than the 

 Hissoa inchoata. Desh., of the Paris basin. 



MESOSTOMA, Deshayes. 

 Mesostoma rugosa, nob. PI. xiii., fig. 13. 



Shell conico-turbinate ; whorls about seven, scalariform, the 

 first three smooth, the rest ornamented with oblique longitudinal 

 plications, which are crossed by five prominent and a number of 

 lesser revolving ridges, giving the whole a cancellate appearance ; 

 the folds on the body-whorl cease abruptly below the middle; 

 aperture sub-circular, dilated, and produced into a short oblique 

 canal ; outer lip somewhat crenulated by the terminations of the 

 revolvino- ridges. 



Length .4 inches. 



Claiborne, Ala. 



Four species in all are catalogued as belonging to this genus, 

 all from the Eocene of France. The above species differs from 

 the M. grata, Desh., of the Paris basin only in the number of its 

 revolving ridges. The Cerithioderma prima of Conrad, from the 

 American Eocene, is a Mesostoma. 



Note. There is some difficulty in determining the priority in 

 the institution of the genera Mesostoma and Cerithioderma. Tate 

 (Appendix to Woodward's "Manual," 1868) quotes the genus 

 Mesostoma from the year 1864, whereas that portion of Deshayes's 

 work, wherein the genus is described, bears the date of 1858. 

 This is the second year of the publication of the entire work, and 

 as the first volume (Lamellibranchiata) was not completely issued 

 until 1860, it is highly probable that the genus was not character- 

 ized prior to that 3*ear. Conrad published his genus Cerithioderma 

 in March, 1860 (J. A. N. S., vol. iv., 2d series), as founded upon a 

 single species C. prima, but as his characterization is vague and 

 veiy meagre, it appears more natural to accept the genus of Des- 

 hayes, which has already been accepted by most conchologists. 



