170 



The Irish Naturalist. 



December, 



Growth of the Radula before and after hatching. 



The growth of the shell was less rapid. Taking its longer 

 diameter as the standard, the juvenile just hatched gave a 

 breadth of 4 mm., at the age of 9 days, 5 mm. ; of 21 days, 

 6 mm. ; at 6 weeks, 8 mm. ; and at 2 months, 9 mm., 

 or about one-third of the diameter of the adult shell. As 

 for the otoliths, about 20 when hatched, they increased to 

 100 after 6 days, to 125 after 21 days, to 175 after 6 weeks, 

 and to 250 after 10 weeks. 



The characteristic dark brown markings of the shell are 

 of slow development. In specimens 6 days hatched dark 

 brown spots and blotches were quite conspicuous, but on 

 opening the transparent shell these markings were found 

 to be confined to the mantle of the animal. K specimen 

 9 days hatched showed the first sign of shell marking in 

 the form of a single pale tawny band encircling the body 

 whorl. Another individual, six weeks old, showed five tawny 

 bands on the shell, the innermost and the third from the 

 centre being twice as broad as the remaining three, which 

 were thread-like. With these bands appeared a few dark 

 spots and blotches. Finally, in a snail ten weeks hatched 

 the dark spots and blotches appeared in large numbers, 

 while the tawny bands on the body whorl were now reduced 

 to two, the first and third from the centre, both of these 

 having much increased in breadth and in depth of colour. 



Sandycove, Co. Dublin. 



1 Of the series of numbers given in this column, the first and second 

 are the result of actual counting ; the remaining five are estimated by 

 a uniform method which understates rather than overstates the number. 



