RADULA OF THE MITRIDtE. 41 1 



strong deeply rooted denticles, then a few serrations or points, 

 and finally blank, denticles 3 and 4 much the strongest ; " break" 

 very pronounced. 



4. /S. limhifera Lam. Durban. Bhachidian 7-cusped on a 

 squarish-oblong base, cusps deeply rooted, short and stumpy, 

 .scarcely projecting above the upper margin ; base straight oi' veiy 

 slightly rounded : laterals with 9-10 short thick denticles which 

 rapidly diminish to mere points, then a long bare space, almost 

 equal to that occupied by denticles ; " break" well marked. 



5. S. lltterata Lam. Andamans. RhacMdian 7-cusped, cusps 

 deeply rooted, the 2 exterior very small, and lying behind, 

 interior 3 equal, projecting considerably beyond the upper margin, 

 next two rather smaller, all rather thick and stumpy ; base quite 

 straight : laterals with 8-9 short, stout, deeply rooted denticles, 

 rapidl}' diminishing to points or serrations, end bare; "break" 

 sharply marked. 



Specimens froui Hilo, Hawaii, and from Scottburgh, Natal, 

 correspond in essentials, but have rather more (11-13) denticles 

 on the laterals. One from Isipingo exhibits the 2 obscure exterior 

 cusps on the rhachidian much more plainly, while the 5 interior 

 are of about equal length. 



6. S. luctuosa A. Ad. Durban. This might well be a specimen 

 of lltterata, except that the cusps, both in rhachidian and laterals, 

 are sharper, and further apart ; there are 7-8 cusps only in the 

 laterals, and beyond them the bare space is very long. 



7. *S'. pellis serpentis Reeve. Mauritius. Radrila small ; rha- 

 chidian 7-cusped, cusps short, rather blunt, deeply rooted, 

 projecting beyond the upper margin, central the thickest and 

 longest ; base straight : laterals with 6 large cusps, rather sharply 

 triangular, some distance apart, then a bare space to the end, the 

 first two only incline slightly inwards ; " break " not very strongly 

 marked. 



This species, in the shape of the lateral cusps, stands rather 

 apart from the others. 



8. S. planilirata Reeve. Suez. Rhachidian 6-cusped, cusps 

 somewhat sharp and narrow, deeply rooted, tips not projecting 

 far beyond the margin ; base straight : latercds with 7-8 deeply 

 rooted cusps, rather near together, gradually diminishing to 

 points, bare space quite considerable ; " break " not very marked. 



9. S. tristis Sowb. Panama. Rhachidian with the upper 

 margin produced at the angles into two curious horns, cusps 8, 

 deeply rooted, the 2 exterior scarcely visible, central 4 the largest, 

 tips scarcely projecting beyond the iipper margin ; base wavy- 

 straight : laterals with 6-7 strong blunt cusps, very deeply rooted 

 on the arched portion, then rapidly diminishing to points, which 

 continue right to the end, no liare part. 



One would expect this species, the only Neotropical repre- 

 sentative of the subgenus whose radula is known, to exhibit 

 difl[erences in structure from the rest, and it does so. 



