102 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



slender, and peculiarly characterized by a lateral bulbous expansion near its 

 base, bearing the retractor muscle. Beyond this bulb the sac is narrow, but 

 gradually expands, and towards its end again very gradually tapers towards 

 the apex, where the vas deferens enters. Its orifice is side by side with that 

 of the vagina. The external orifice of the system is under the mantle. 



I found no dart in the bulb-like organ attached to the penis sac. It proba- 

 bly is a form of prostate. 



The Texas specimens have a much thicker shell than those from Illinois. 



Zonites caducus, PFR. 



Shell umbilicated, depressed, fragile, shortly striate, white with a reddish 

 horn-colored epidermis ; spire slightly elevated, apex delicate ; whorls 5^, 

 Fig. 22. rather convex, the last much broader, rather flattened 



below, excavated around the tunnel-like minutely closed 

 umbilicus ; aperture large, obliquely oval ; peristorne 

 simple, thin, with ends approaching, joined with a 

 very light callus, the columellar one scarcely broadened. 

 Zonites caducm. Greater diameter 27, lesser 22 mill. ; height, 14 mill. 



Helix caduca, PFEIFFEE, Mon. Hel. Viv., I. 89, etc. REEVE, Con. Icon., 530. 

 W. G. BIXNEY, Terr. Moll., IV. 105. 



Hyalina caduca, TRYON, Am. Journ. Conch., II. 248 (1866). 



Zmiites caducus, W. G. BINNEY, L. & Fr.-W. Sh., I. 287, Fig. 513 (1869). FIS- 

 CHER and CROSSE, Moll. Mex., 163, PI. VII. 3 a, 3 d (1870). 



Admitted in the catalogue on the authority of Pfeiffer (Roemer's Texas, 

 455), who quotes it from New Washington. It is a Mexican shell : a specimen 

 from that locality is figured (Fig. 22). 



The dentition of Z. caducus is known only by the description and figure of 

 Fischer and Crosse (Moll. Mex. et Guat., 149, PI. VIH. Figs. 13-16). There 

 are 75 1 75 teeth, with 5 laterals. 



Zonites laevigatus, PFEIFFER. 

 Vol. HI. PL XXXH. 



Shell somewhat convex, oftener depressed ; epidermis greenish horn-color, 

 shining, thin ; whorls 5, rather flattened, rapidly enlarging, with beautiful 

 and regular oblique strise and revolving microscopic lines ; the last whorl ex- 

 panding towards the aperture, not descending; aperture transverse, broadly 

 lunar, ample, with a testaceous deposit within ; peristome thin, acute, straight, 

 extremities approaching, its lower extremity inserted into the centre of the 

 base, and somewhat reflected; base smooth, perforate. Greater diameter 18, 

 lesser 15 mill. ; height, 9 mill. 



Helix favigata, PFEIFFER, Mon. Hel. Viv., I. 64 ; III. 67 (excl. syn.) ; in 

 - CHEMNITZ, ed. 2, II. 106, PI. LXXXIV. Fig. 17-19 (excl. syu.). REEVE, 



