o2 MOLLtJSCOtrs AXIMALS. 



as depeudiug on microscopical observation ; but not to use along witii 

 otbers a cbaraoter manifestly connected witli distinctive habits of life, 

 would be to negleet means within our reach for determining natural 

 affinities, and as knowledge on the subject has rapidly increased would 

 no longer be thought of. G-reater characters taken from the br;iin and 

 the absence of placentation, separate the Opossums from the Carnivora, 

 but their dentition establishes an important relation of analogy, giving 

 these animals the same position in the nonplacentated or Lyeucephalous 

 sub-class, which the Carnivora hold in the Gyrencephalous and the 

 lusectivora in the Lissencephalous. The objections or doubts of Mr. 

 "Woodward have not then any force which should prevent general 

 attention to the structure of the Odontophore as an aid in classi- 

 fication. 



I confess that I cannot see the advantage gained by giving names to 

 the principal varieties in the disposal of the teeth as has been done by 

 Trosehel and Dr. J. E. Gray. Several of the varieties seem to me to 

 be very slight modifications of each other ; none of them could of itself 

 alone give character to a natural group of animals, and I cannot perceive 

 that the new terms aS"ord any real assistance in stating the tacts con^ 

 cisely and intelligibly. Along with the peculiarities of the Odontophore 

 must be noticed the form of the muscle in which it is contained, and 

 the absence or presence, form and markings, of what have been called 

 the buccal plates. 



Important characters are also derived from the number of the tentacles, 

 the position of the eyes, the form of the foot and other circumstances 

 relating to the animal. It is to the proper combination and subordination 

 of these characters, giving prominence to general form and habit ia 

 distinguishing families, and in doubtful cases placing the creature in 

 the group to which, considering all the characters it seems to have the 

 nearest affinity, that we must look for a good natural system. In the 

 higher divisions we look for fewer but more important distinctive marks 

 accompaned by a certain recognisable aspect of each group, and its 

 expression of one of those tendencies of development, five of which have 

 been pointed out as the sources of the leading differences under each 

 general type. 



I cannot help here desiring to commemorate the obligations of all 

 who study the MoUusca to Dr. J. E. G-ray of the British Museum, for 

 his important services to this branch of Science, as indeed to all depart- 

 ments of Natural Science. 



