433 Dr. J. E. Gray on the genus Assiniinia. 



XXXV. — On the Genera of Mollusca, and on the Genus Assiminia 

 in particular. By Dr. J. E. Ghay, F.R.S. &c. 



To the Editors of the Annuls of Natural History. 



Gentlemen, 



I AM induced to forward the following observations, occasioned 

 by Mr. Clark's reply to my note on the genus Assiminia, more 

 on account of their general application, than as simply bearing 

 on Mr. Clark's paper. Mr. Clark must, I think, be almost the 

 last remaining member of the Montaguan school of British ma- 

 lacologists who have done so much to increase our knowledge of 

 the Mollusca of our shores. Unfortunately, however, he is not,like 

 most of his colleagues, satisfied simply to describe and record the 

 structure and habits of the species falling under his own observa- 

 tion, but wishes, without taking the trouble to study those found 

 in other parts of the world than our own little island, to form 

 a system of his own ; to decide on the manner in which the Mol- 

 lusca of all the world should be arranged ; to give an ex cathedra 

 opinion as to the propriety and value of groups of species of 

 which he has probably only seen a single small and perhaps 

 abei'rant example ; and to determine on the validity of a specific 

 distinction by the observation of a collection of small extent, 

 collected in a single locality. Malacologists must, however, 

 always be thankful for the labours of the describer of the animal 

 of CcEcum, Dentalium, and several other interesting genera, al- 

 though it may be permitted them to wish that he would not 

 publish his descriptions until he had made up his own opinions 

 as to the accuracy of his observations, and not correct them, and 

 then have to correct his corrections back to his old statement, as 

 is to be found in more than one instance in his papers and work. 

 There can be little doubt that distinct kinds (or as we gene- 

 rally call them, species) of animals exist in nature. It is the 

 chief occupation of a naturalist to observe the external charac- 

 ters, the anatomical structure and the peculiarities in the habits 

 and manners of each of these kinds or species, and to compare 

 them with each other, both as individuals and as collected into 

 groups. It is equally indisputable that certain kinds, or species^ 

 have important characters in common, and it has been the cus- 

 tom from the earliest times to collect such kinds as have such 

 common characters into groups, and to divide these great groups 

 into smaller and smaller groups by such characters as are common 

 to each ; and these groups, according to their relative importance, 

 have been called classes, orders, families, genera and subgenera; 

 but few naturalists, I believe, regard the lower at least of these 



