MOLLUSCA OF PLYMOUTH. 



417 



increase in the number of lateral teeth from 13 to 16 on each side, 

 passing from the front to the back of the radula. 



I have seen, through the kindness of Mr. H. M. Gwatkin, the 

 radula of a Guernsey Aplysia 9*5 mm. long by 6 mm. broad, dis- 

 tinctly intermediate in its characters between Nos. 9 and 10 on the 

 one hand, and Nos. 11 and 12 on the other. Formula (21"1*21) x 

 53. Teeth resemble those of 9 and 10, but the breadth decreases 

 from 037 mm. in front to 034 behind, without the anterior 

 crescendo. This poiuts also towards the unity of the two " spe- 

 cies." 



