378 A MANUAL OF AMERICAN LAND SHELLS. 



of only one eighth of an inch, forms a beautiful variety, and has been 

 thought to be a distinct species. 



The form known as volvoxis is found on the Atlantic coast of Florida 

 and Georgia. It is thus described by Pfeiflfer. The synonymy is also 

 given in full. I believe it to be a variety of septemvolva. 



Shell umbilicatedj orbicularly convex, thin, reddish horn-colored, 

 pellucid, with regular rib-like striae ; spire very short, convex ; whorls 

 7, convex, regularly increasing, the last larger above than the rest, an- 

 gular, below the angle inflated, striated, and shining; umbilicus large, 

 regular, in which the whorls regularly decrease, excepting the last, 

 which is very broad ; aperture rather large, kidney-shaped ; peristome 

 thickened within, reflected, its terminations joined by a short, triangular, 

 tooth-like callus. Greater diameter 9 lesser 8°"" ; height, 4™'". 



Melix rolvoxu, Parreyss, in Pfeiffer, Symb., iii,80; Mon. Hel. Viv., i, 409; in 

 Chemnitz, ed. 2, i. 379 (1846), pi. Ixvi, figs., 4-6 (1849).— Reeve, Con. Icon., 

 No. 1237 (1K54).— W. G. Binney, Terr. Moll. U. S., iv, 92, pi. Ixxviii, fig. 17.— 

 Bland, Ann. N. Y. Lye, vii, 135. 



Folygyra volvoxis, Tryon, Am. Jouru. Concb., iii, 159, pi. xi, fig. 25 (1867). 



Jaw long, narrow, slightly arched ; ends attenuated, bluntly rounded ; 

 anterior surface with 7 stout, distant ribs, creuulating the cutting edge. 



There are 28-1-28 teeth, with 9 laterals on the lingual membrane of 

 the large form (Terr. Moll., V, Plate VI., Fig. L). The small form, with 

 5 whorls, differs only in having somewhat fewer teeth. The form known 

 as volvoxis does not differ excepting in having fewer marginals ; Jack- 

 sonville, Fla., specimens have 20-1-20 teeth. 



The Museum of Comparative Zoology at Cambridge has a reversed 

 specimen of P. septemvolva. 



Terr. Moll., V, Plate XV, Fig. H, represents the genital system of the 

 large form of this species. It is characterized by its extreme length, 

 as would be expected from the form of the shell. The vagina is ex- 

 tremely long and narrow. The genital bladder is elongated-oval, on a 

 short, slender duct. The penis sac is very long, attenuated to a point 

 above, where the retractor muscle is inserted. 



The digestive system is also very much elongated. The oesophagus 

 especially is excessively long, as are also the ducts to the salivary 

 glands. 



This species is extremely common all over Saint Augustine and its 

 vicinity. The large form I found almost restricted to the moat of the 

 old fort, especially at the foot of the main western wall. 



