202 



M I i I ; I -TIC VARIATION. 



[I'AKT I. 



divided, but tin- di\i-i..n is gradually lost towards the middle of the 

 ja\v ami tli.- .'Menial plates are without trace of division. C. 8. .M. 



l'i<.. 71. The lower jaw of a Selachian, No. 400. The proximal ends shewn 

 (enlarged). The right is reversed for comparison with the left. 



OF A GASTEROPOD. 



The following e.N.-nnple of Meristic Variation in the teeth 

 of a Mnlluscnn odmituphore may be taken in connexion with 

 the subject of teeth, though the structures are of course wholly 

 different in nature. For information on this subject I am in- 

 debted to the Rev. A. H. COOKE. 



( leu. -rallv speaking the number and shapes of the radular 

 teeth ait- \er\ characteristic of the different classificatory divi- 

 There arc however certain forms in which a wide range 



-..ns. 



of Variation is met with; of these the case of Buccinum inidatum is 



the most 



'401. Buccinum undatum. In most specimens the number of 

 denticles "n ih<' central plate is ."> 7 and on the laterals 3 4. 

 In -1 -ecinicns from Haniiiierfest and Vardo the teeth were 



Lateral plates. Cases. 



4 8 



4 12 



4 2 



4 1 



4 1 



3 & 4 1 

 3& 4 1 



4 & : 1 



. Ges., vi. 1879, p. 2:>7. 



Central plate. 

 5 

 6 

 7 

 68 



9 



(i 

 7 

 8 

 from FKIKLE, Julu-L. </<'{. 



