Manchester Memoirs, Vol. xlvii. (1903), No. 0. 5 



connection with this examination I desire to acknowledge 

 the courteous assistance of Mr. A. R. Nichols. 



On comparing this description with that of Girard 

 (1890, p. 251) the principal points of difference are seen to 

 be as follow : — 



1. A slight divergence in the outline of the fin. This, 



I think, may be accounted for partly by the fact 

 that this organ is variable in shape, partly by the 

 bad condition of Ball's type (see above), and 

 partly by the fact that a correct outline of the 

 fin is not so easy to draw as might be imagined, 

 because it is often so bent and twisted as not to 

 be readily laid down on a plane surface. 



2. The funnel-mantle connective is rather longer than 



indicated by Girard's phrase " s'inscrivant dans un 

 triangle equilateral." 



The typical male specimen of Girard agrees fairly 

 well in proportional dimensions with that of Ball ; the 

 former is considerably larger, the length of the mantle 

 measuring 130 mm. as against yj mm. 



The more important measurements reduced to per- 

 centages of the length of the mantle are as follow :— 



Mantle, length 



„ breadth 

 Head, breadth 

 Fin, length 

 „ breadth 



Arm, first 

 ,, second 

 ,, third 

 ,, fourth 



Right. 



65 

 88 



81 

 71 



Girard's 

 type. 



100 



45 

 32 



50 

 81 



Left. 

 ... 65 

 ... 84 

 ... 83 

 ... 69 



BalPs 

 type. 



100 



45 . 



30 



39 

 87 



Right. 



84 



104 



91 

 78 



Left. 

 78 



97 

 91 



