RADULA OF THE MITRID.E. 417 



sometimes two coalesce into one : laterals set with 20-24 tiny 

 sharp denticles on a slightly curved framework, not greatly differ- 

 ing in size except at the extreme end, where they become very 

 small. 



4. M. 2^roscissa Reeve. Karachi. Rhachklian 11-12-cnsped, 

 cusps tiny, sharp, close together, equal in size, upper margin 

 slightly curved, framework very narrow: laterals with 13-14 

 cusps, the 2 or 3 innermost rather short and stumpy, the rest 

 larger and sharp, none inclining inward ; they gradually diminish 

 to the extreme end. 



5. M. pura A. Ad. China. Rhachklian 6-cusped, the 2 ex- 

 terior below tlie plane of the rest ; margin straight, base slightly 

 rounded: laterals v^^'xth 12-13 sharp denticles, set rather apart 

 from one another, gradually diminishing to the end. 



This and the following group probably represent separate 

 branches from the parent stem. 



Group (10) of scabriuscida. 



Radula with rhachidian and laterals set with numerous small 

 sharp cusps ; framework of rhachidian narrow, deeply arched, 

 tips curving upward ; framework of laterals narrow, arched, then 

 straight. 



1. M. circula Kien. Pui^ban. Rhachidian and laterals set 

 with very numerous tiny denticles, all about the same size. The 

 specimen is in bad condition, preventing the denticles from being 

 counted. 



Text-fisfure 16. 



Lateral and rhacliidian tooth oi Mifra scahriuscida L. 



2. M. scahriuscida L. XJpolu. Rhachidian with 30-32 tiny 

 denticles, not deeply rooted, gradually diminishing towards the 

 ends ; framework nari^ow at tips, deeply curved, tips bare and tvxrn- 

 ing slightly upward : laterals with about 32 similar denticles set 

 closely together, interior end bare of denticles, they continue to 

 the exterior end, gradually diminishing in both directions. 



The form of the rhachidian in this group, corresponding closely 

 as it does with that of Turricida, forms an interesting link 

 between the radula of that genus and that of Mitra, Avhile the 

 laterals, on the other hand, resemble in miniature those of Mitra 

 proper. 



Genus Yexillum Bolten (olim Turricida [Klein] auctt.). 



As pointed out long ago by Gray (3, 4), the laterals in Vexillum, 

 instead of being broad and comb-shaped, with manysharp denticles, 



