tW THE NAUTILUS. 



The radula of P. tnrrel is approximately 14.5 mm. long, and 

 1 mm. wide, and contains in the vicinity of 2oJ row.s of teeth. 

 The central tooth and the four laterals on each side are perpen- 

 dicular to the long axis of the radula, the rest of the row com- 

 prised of approximately 100 uncini, curves back toward the 

 posterior end of the radula. The central tooth (pi. 4, fig. 1, c. ) 

 has a very slight cusp at its summit. The laterals (i, ii, iii) 

 possess very strong cusps which are not denticulate. The 

 major lateral (iv) cannot be described as denticulate, the cutting 

 edge being merely slightly sinuous. In this respect the radula 

 of Priotrochdtelln differs from that of any of the other Heli- 

 cinidae. If this major lateral is composed of two teeth, they 

 are so firmly interlocked that I have been unable to separate 

 them. The uncini (Fig. 1, u) (Fig. 2) are numerous and 

 densely packed. The innermost (1, 2) are simple, possessing 

 but one cutting edge, later (38, 39) becoming bidentate. In 

 the 45th (45) tooth of the radula figured, the inner denticle is 

 again divided, and the increase in the number of denticles con- 

 tinues to about the 98th row where the cusp is twelve-denticled. 

 The curve of the outer edge of the radula causes the cutting 

 edge of the outermost uncini to be turned inward toward the 

 center of the radula and parallel to its long axis. The three or 

 four outermost uncini are very broad flat plates and the denti- 

 cles entirely disappear. 



The radulae of P. coiistellata and P. stellata are very similar to 

 that of torrei excepting in the central teeth. In P. stellata 

 (Fig. 4) the central tooth is large, with a very strong broad 

 cusp. In P. coiistellata (Fig. 3) and in P. torrei the central 

 teeth are very similar in size, differing only in the shape of a 

 very small cusp. There do not seem to be any constant differ- 

 ences in the radulae of the Priotrochatella excepting in the cen- 

 tral teeth. 



Summary (1). The radulae of the three species of Priotro- 

 chatella exhibit sufficient differences in structure from other 

 groups of Helicinidae to sustain the raising of Priotrochatella to 

 generic rank. 



Suramary (2). The similarity of the radula of P. torrei to 

 that of P. constellata is of sufficient importance to lend consider- 



