ON THE RADULA OF THE MITRID.E. 405 



26. The lladnla of the Mitridfe. 

 By the Rev. A. H. Cooke, Sc.D., F.Z.S. 



[Received October 16, 1919 : Read November 18, 1919.] 



(Text-figures 1-18.) 



Fifty years have passed suice F. H. Troschel pubhshed his great 

 work on the radul?e of MoUusca (11), and, during the interval, 

 the number of Mitridte whose radulfe have been investigated may 

 be counted on the fingers of one hand. From one cause or another, 

 Troschel's work on the group contained some serious errors of 

 misstatement, which have been copied into the subsequent 

 Manuals dealing with the Mollusca, e.g., those of P. Fischer (1) 

 and Tryon (12). Troschel figured, as belonging to Imbricana, a 

 radula closely akin to that of Vasiim, and placed the subgenus 

 ■close to the Turbinellid?e ; he held that StrigateUa had a radula 

 whose form difl^ered widely from that of the typical Mitridse, and 

 was closely allied to that of Turricula (now VexiUum Bolt.), while 

 the true form of the VexiUum radula was imperfectly described 

 by him. 



The recent acquisition, by the British Museum (Natural 

 History), of the vast collection of radulae formed by the late 

 Prof. H. M. Grwatkin, enables fresh light to be thrown on this 

 and other groups, while the results can be checked, in part, by 

 the collections which he gave, dming his lifetime, to Cambridge 

 and other Universities. 



Troschel figured and described 13 species of Mitridfe [Cylindra 

 1, Mitra proper 5, Tmbricaria 1, StrigateUa 2, Turricida {Vexil- 

 lum) 4 : Volutomii7-a is now more correctly placed with the 

 Yolutidae. The Gwatkin Collection contains 14 VexiUum and 37 

 belonging to other groups, of which 51 only 4 were known to 

 Troschel, and nearly all are new to Science. 



In Mitra proper the radula is remarkably broad in proportion 

 to its length, a feature due to the extreme width of the laterals. 

 For instance, in adult specimens, we have : — 



adusta Lam. Length in mm. 5'0 ; breadth in mm. 1*5. 



cardinalis Gmel. ,, ,, 5"0 ,, ,, 1"2. 



digitalis Chem. ,, ,, 5'0 ,, ,, 1"4. 



episcopalis L. ,, ,, 7*0 ,, ,, 2*0. 



glabra Swains. ,, ,, 6*5 ,, ,, 1-6. 



papalis L. ,, ,, 5*0 ,, ,, I'O. 



The number of rows of teeth varies : — 



ftrZusia (full-grown) has 76-|- nas3ent rows. 



„_ (young) „ 64 



cardinalis ,, 61 ,, ,, 



,, (another spec.) ,, 67 „ ,, 



28* 



