.392 MOLLUSCOUS ANIMALS. 



the direct interpretation of which is that the centre is a point on the 

 curve ; and the determinant (8) becomes 

 M, w, v 



w, V, u' = . 



V, u', w 

 If simultaneously with this condition, we have also 



KLsm^A + anal 4- =0, 



the curve breaks up into two parallel lines. 



J. B. C. 

 Toronto, December, 1867. 



MOLLUSCOUS ANIMALS. 

 NO 2. 



BY REV. PROFESSOR HINCKS, F.L.S. 



In my former paper on Molluscous animals I had to deal with a part 

 of the subject where I might reasonably consider the materials for judg- 

 ing within my reach, and where I could maintain my opinions with some 

 confidence. In proceeding to the subdivision of the several classes, I feel 

 my task to be far more difficult and more uncertain in its results. It is true 

 that in some of the classes orders have been proposed, and in the smaller 

 classes the families answer the same purpose ; but in some cases the 

 attempts made, even by those whose authority is considered very high, 

 are far from being satisfactory, and in others there can scarcely be said 

 to have been any attempts made. A classification complete in all its 

 steps is required for introducing students, most easily, to a knowledge of 

 the structure and mutual relations of the creatures, and I have felt the 

 need of it to such an extent as to be drawn to attempt something, whilst 

 I feel that though I have very long interested my self greatly in this divis- 

 ion of the Animal kingdom, my distance, for some years past, from the 

 sea, from large collections, and from the most valuable books, throws 

 great difficulties in my way, and prevents my feeling much confidence in 

 what I have to offer. To begin with the class Tunicata, both the sub- 

 classes have been divided by good authorities into Orders, in each case, 

 five in number, and seemingly well-founded, though the analogies usually 

 perceptible between the divisions, corresponding in position, here escape 



