124 THE NAUTILUS. 
Aperture mainly basal, lunate, with a lining of white callus a 
short distance within, heavier and bearing a small tooth on the 
columellar slope, and a rather short white lamella toward the outer 
part of the base. Lip-edge thin and acute, suddenly expanded at 
the columellar insertion, half covering the umbilical perforation. 
Alt. 7, diam. 84 mm. 
Alt. 5%, diam. 84 mm. 
Described from thirty-four specimens, from Knoxville, Tenn. ; 
Citico, Monroe Co., Tenn. (A. G. Wetherby); Knox Co., Tenn. 
(Mrs. Geo. Andrews), and Nashville, Tenn. (G. A. Lathrop). 
Variation is observed in the height of spire and the degree of de- 
velopment and length of the basal lamella. It is most nearly allied 
to G. ligera and G. cerinoidea, being smaller than the former, with 
different aperture armature, and larger, duller and more elevated 
than the latter. 
My attention was first called to this form by Mr. A. G. Weth- 
erby, although specimens from Nashville had long been in the collec- 
tion of the Academy of Natural Sciences. It seems to be a fairly 
common species, probably confined to the “ Cumberland Subregion ” 
of Binney. 
In describing this form, it is a pleasure to add that so competent 
an observer as Mr. Wetherby agrees with me that it is a new spe- 
cies; for I suppose no living naturalist is more experienced than he 
in dealing with the shells of the beautiful mountain region it in- 
habits. 
NEW NORTH AMERICAN PISIDIA. 
BY DR. V. STERKI. 
Pis. trapezoideum n. sp. 
Mussel of moderate size, rather much inflated, irregularly quad- 
rangular in outline; beaks slightly posterior, rather large and prom- 
inent, more or less distinctly flattened on top ; superior margin little 
curved, with the scutum and scutellum well developed and marked 
by distinct angles where joining the posterior and anterior margins ; 
the former truncated perpendicularly, and with an obtuse, rounded 
angle where passing into the moderately curved and comparatively 
long inferior margin; antero-superior margin little curved or 
straight and meeting the inferior in a well marked somewhat 
