Notes on Lingual Dentition of MoIIusca. 287 



Helicina occulta, Say. 



Lingual membrane long and narrow. Teeth 00.5.1.5.00, in 



transverse, arching rows. Centrals upright, longer than wide, 



widest at the horizontal base, slightly narrowing towards the 



apex, which is nearly as wide as the base, broadly recurved and 



Fio. a 



Lingual dentition of Helicina occulta, Say. 



denticulated at its cutting edge. First lateral oblong, shorter 

 than the central, rounded at base, narrowed towards the apex, 

 which is broadly recurved and denticulated ; this lateral is in- 

 clined obliquely from the central, its apex being reflexed in the 

 same direction. The second lateral resembles the first lateral in 

 every particular, but is much less wide. Third lateral perpendi- 

 cular, longer than broad, triangular, its apex small, reflexed and 

 denticulated. Fourth lateral very long, irregular, jaw shaped, 

 its lower edge for one-half its length furnished with four strong, 

 large, acute, beak like denticles; the left end of this lateral is 

 produced in a horizontal direction, at right angles to the direction 

 of the balance of the tooth, is excavated above and below, and in 

 some instances appeared to have a wing-like expansion behind 

 the uncini. Fifth lateral quite small, subcircular, its apex broadly 

 refleeted and denticulated, the whole tooth fitting into the upper 

 excavation of the horizontal portion of the fourth tooth. The 

 uncini, more than twenty-five in number, are long, slender, 

 crowded, the apex reflexed and continued in three fringe-like 

 denticles. 



There seems to be great uniformity in the teeth of the different 



