3 30 American Seashells 



I to 1% inches in length. Primary ribs i6 to i8, fairly distinct in 

 the young stages; sculptureless in the senile stage. Round in cross-section. 

 Chalky-white when eroded. Common from 20 to 1,000 fathoms. 



Dentalium autillarum Orbigny Antillean Tusk 



South half of Florida and the West Indies. 



About I inch in length, roundish in cross-section. Primary ribs 9, but 

 increasing to 1 2 near the middle and finally with 24 near the aperture. Mi- 

 croscopic, transverse lines between the ribs. Color opaque-white, rarely 

 reflecting a greenish tint. Encircled with weak, zigzag bands or splotches 

 of translucent gray. 



Dentalium pilsbryi Rehder Pilsbry's Tusk 



Figure 69d 



West Florida and Brazil only. 



% to 1% inches in length, roundish in cross-section. Primary ribs 9, 

 with a smaller, weaker, rounded, secondary rib appearing between each. All 

 ribs fade out toward the anterior end. Intercostal spaces flat, crossed by 

 coarse growth lines. No transverse, microscopic sculpture. Color opaque- 

 white; without gray splotches. Formerly known as D. pseiidohexagonum 

 Henderson 1920, not Arnold 1903. Uncommon from 2 to 5 fathoms. 



Dentalium pretiosum Sowerby Indian Money Tusk 



Figure 6gi 



Alaska to Lower California. 



About 2 inches in length, moderately curved and solid; opaque-white, 

 ivory-like, commonly with faint dirty-buff rings of growth. Apex with a 

 short notch on the convex side. A common offshore species which was used 

 extensively by the northwest Indians for money. 



Subgenus Fissidentalium Fischer 1895 

 Dentalium floridense Henderson Florida Tusk 



Southeast Florida and the West Indies. 



2 to 3 inches in length, roundish in cross-section. Shell hard and yel- 

 lowish white. Apex hexagonal with concave spaces between. Ribs increase 

 to 24 anteriorly and are rounded, equal-sized and crowded. There is a long, 

 narrow apical slit on the convex side. Rare from 35 to 100 fathoms. 



