RADULA OF OPISTIIOBRANCHIATA 



229 



Proneomenia and Zejndomenia have about twenty falciform 

 teeth, much larger at one end of the radula tlian the other ; 

 formula, 0.1.0. " 



Opisthobranchiata. — The radula, of tlie Opistholn-anchiata 

 is exceedingly vaiiahle in shape, size, and number and character 

 of teeth. Not oidy do allied families differ greatly from one 

 another, but allied genera often possess radulae widely distinct 



in plan. Thus, among the i'olycevidae, GoniodorU lias no central 

 tootli, one large lateral and one marginal (form. 1,1.0.1.1); 

 Dorldunculus the same, witli live marginals (form. 5.1.0.1.5); 

 LiuneUidoris one each of median, laterals and marginals 

 (1.1.1.1.1); Idalia, Aiicvln, and Tlirrwera the same as Goniodoris ; 

 Crimora several each of laterals and marginals. Even species of 

 the same genus may differ ; thus the formula for Aeoli's papillosa 

 is 0.1.0, l)ut for yie. Landshergi 1.1.1 ; for Fhiline aperta 1.0.1, 

 but for Fhiline 2yncinosa 6.0.6. 



It must not be forgotten, however, that a simple repetition of 

 the same tooth, whether lateral or marginal, does not necessarily 

 constitute an important characteristic, nor does the presence or 

 al)sence of a central tooth. In most of the cases mentioned above, 

 the difference in tlie nundier of laterals and marginals is due to 

 the multiplicaticiu of identical forms, wliile the central tooth, when 

 present, is often a mere plate or narrow block without cusps, 

 whose presence or al)sence makes little difference to the character 

 of the radula as a whole. 



There appear to Ije three well-marked types of radida among 

 the Opisthobranchiata. 



(a) l{;idu];i with a single^ strong central tooth, rows few. 



