54 



Arenicolidae 



has, when unworn, a slender and slightly upturned tip (Fig. 29), 

 which, however, is soon worn away when the crotchet comes 

 into use. Fig. 30 represents the latest growth-phase found 

 in the crotchets of these species. 



Fig. 26. — A. cristata. A, Crotchet from a young adult, 48 mm. long ; B, From a specimen 130 mm. 

 long ; C, From a specimen 250 mm. long ; D, A worn crotchet, and E, The tip of an unused crotchet, 

 from a specimen 330 mm. long. 



The crotchets of the larval and post-larval stages do not afford 

 any reliable help in diagnosis, their form and characters seem to 

 change so rapidly during the very early phases of growth that 

 larval or post-larval crotchets of the same species, but of different 



