194 CRUSTACEANS. 



Amidst the numerous animals comprehended under the common 

 character of Crustaceans, the general form of so many is so different from 

 that of others, as by comparison to afford the best guide to their position 

 in the Systema Naturae, and the discrimination of their genera. 



I have not been so fortunate as to obtain and preserve a sufficient 

 number of specimens and varieties, as to shew the essential distinctions 

 among them, or to determine either the transitions or analogies. Some, 

 indeed, I have had in profusion ; but, on the other hand, a single speci- 

 men has constituted my whole stock, throughout, which the research of 

 twenty or of thirty years or longer has not augmented. 



In several instances, therefore, the only auxiliary that I can offer is 

 correct representation from the life. Where opportunity has granted 

 more, I have eagerly availed myself of it ; but, I candidly acknowledge, 

 that I have been always more solicitous about obtaining facts, and multi- 

 plying species, than founding systems, which latter are less within the 

 province of the practical naturalist. 



Hence, perhaps, do many restrict their whole labours to the history 

 of a single genus, or perhaps to that of a single species. 



Among the more noted forms of the body, a large section of the 

 Cancer tribe is exhibited as entirely triangular or sub-triangular, in 

 various modifications. 



I know not with what justice, but it has appeared to me that these 

 are always somewhat more delicate than the others, a fact to be deter- 

 mined or confuted only by numerous subsequent observations. 



The disproportionate parts certainly render the preservation of en- 

 tire subjects more precarious. 



D. 1. CANCER (INACHUS) DORSETTENSIS. Plate XLVI. fig. 4. 



When the general appearance and character of a subject are so pro- 

 minent, that to mistake it for any other is impossible, I cannot see that 

 enumeration of trivial peculiarities is of the slightest importance. 



The form and dimensions of this species, which is scarce, are well 

 expressed in its representation, Plate XLVI. fig. 4. 



Specimens have survived during many months. They dwell to- 

 gether in peace. 



