122 Marine Shells of the Western Coast of Florida 



Odostomia impressa^i* Say PI. 23, fig. 162 



Alt., 4 mm. Shell milky white, elongate-conic; small nuclear 

 whorls partly embedded in succeeding turn; six or seven flattened- 

 convex whorls, outline indented by sculpture; sutures channeled; 

 themselves impressed with delicate spiral striations; aperture ovate, 

 whorls sculptured with three equidistant, deeply cut spiral grooves, 

 simple, angled above; outer lip sharp. The outer lip of adult shells 

 is somewhat flaring, aperture narrowed within. Columella has one 

 oblique fold. Base shows about seven narrow spiral grooves. 



0. impressa is generally found about oyster bars among clumps 

 of oysters. 



Egg capsules of Odostomia impressa Say PI. 46, figs. 322a, b 



Odostomia trifida^is Totten PI. 23, fig. 163 



Alt., 4 to 5 mm. Shell white, glossy, thin, translucent; yellow- 

 ish penostraciHTi; conic-ovate; nuclear whorls small, partly embed- 

 ded m followmg turn; eight whorls, moderately convex, slightly 

 shouldered at summit; sutures distinct; sculpture of three deeply 

 cut inequidistant, and one faint spiral line; aperture elongate-oval, 

 upper angle acute; outer lip thin, its interior showing reverse of ex- 

 ternal sculpture; columella with one strong oblique fold above 

 middle; base rounded, narrowed below, impressed with about 10 

 unequal, inequidistant striae; operculum corneous, brown. 



Inhabits mud and sand flats, often among sea grasses. 



Subgenus CHRYSALLIDA Carpenter, 1856 

 Odostomia seminuda"^" (C. B. Adams) PI. 23, fig. 164 



Alt., 3.75 to 4 mm. Shell elongate-conic; milky white, glossy; 

 about two smooth nuclear whorls obliquely embedded in next suc- 

 ceeding whorl; six or seven slightly convex whorls, shouldered at 

 summit, body whorl rounded; sutures distinct; whorls sculptured 

 between sutures by axial ribs cancellated into beads of nodules 

 by four low, broad, equidistant ridges; aperture somewhat auriform, 

 outer lip simple, thick within, thin at edge, showing external sculp- 



-!■* Lat., impressus, pressed. 

 -^^ Lat., trifidus, three-cleft. 

 -I'^Lat., sfmi, half; nudus, naked. 



