Trof, Hall on a New Crustacean* 443 



creatures to JEJchinoderms, their radiated structure, and their place 

 in the system as two of the classes of the Radiata. 



It may be objected that these views savour of the arbitrary 

 methods proposed by MacLeay and Swaiuson. If, however, there 

 is system in nature, it must admit of some general statement ; 

 and the time must come when naturalists will be obliged, by the 

 necessities of the case, to search for and apply such general views. 



Specialists will object that they must have more subdivisions of 

 animals than those above admitted ; but they have full scope for 

 this in the formation of families, orders, and genera, without at- 

 tempting to disintegrate our higher groups. The family, in par- 

 ticular, as distinct from the order, is a group of great value, and 

 to the cultivation of which their attention might be very properly 

 directed, more especially since the genus is fast losing its impor- 

 tance, from the tendency to erect every little group of species, 

 distinguished by some minute structural peculiarity, into a new 

 genus. Since, however, the greater part of these are clearly 

 nothing but sub-genera, it might be well to have some arrange- 

 ment which might enable them to be recognized for purposes of 

 determination, while the grand generic unity should be maintained 

 by retaining the name of the genus proper, in the nomenclature, 

 with a mark or number to indicate the sub-genus. 



The views thus slightly outlined are not of yesterday ; but have 

 resulted from much thought on the subject. They are, however, 

 thrown out merely as suggestions for the consideration and criti- 

 cism of naturalists, and in the hope that they may, at least in 

 part, be found to harmonize with the true order of animal nature 

 in its lower forms, as the progress of discovery brings this more 

 distinctly into view. 



J. W. D. 



ARTICLE XLll.— On a new Crustacean from the Potsdam 

 sandstone. By Trof. James Hall. A Letter addressed to 

 Principal Dawson, dated Albany, Zlst October, 1862. 



I have been much interested in reading your observations upon 

 the tracks of Limulus in sand, and comparisons with the tracks 

 in the Potsdam sandstone ;* more especially as these observations 

 connect themselves in a remarkable manner with a recent discov- 

 ery of my own ; and a question may arise as to whether you have 



* Canadian Naturalist for August, 1862. 



