40 



MOLLFSCA OF THE ' CHALLENGER ' EXPEDITION. 



three small laterals occurs a single largish bicuspid tooth, not 

 nearly so formidable a weapon as that of Scutus australis, which is 

 enormously larger, more curved, and tricuspid. Beyond these, as 

 m Grray's figure, but very much more numerous and more crowded, 

 are an infinity of small hooked laterals. Attaching very little 

 value to systems of classification of Mollusca based on dentition, I 

 should have hesitated to follow Mr. Dall in separating this group 

 from Lepeta ; but there is one fact which probably is a sufficient 

 reason for a step otherwise much to be deplored, viz. that in Coc- 

 culina the long slope of the shell is in front, a feature which the 

 genus shares with Propilidium in common with the whole of the 

 " fissured Limpets," and which contradicts the common rule for 

 the unfissured Limpets, tha.t the short slope is in front. 



Dentition of Coceulina angtdata, Wats., highly magnified. 



