212 CRUSTACEANS. 



of the Astacus mar'ums, other genera dwell either in this or in foreign 

 countries, whereby the transition might be more naturally and effectually 

 shewn, but satisfactory illustrations will be probably found in the two 

 we have just named, the Adacus Norveijicus and Astacus marinus. With 

 the last we are most familiar, it is readily and easily obtained by man}', 

 who prefer beholding every object itself to confiding in the correctness of 

 description. Perhaps this is always the best method of acquiring know- 

 ledge. 



No better example of human ignorance can arrest our progress than 

 contemplating the formation of the animal before us ; to describe its 

 various parts is scarcely within the power of language, and to explain 

 the use for which the Governor of the Universe designs them, surpasses 

 the narrow and contracted sphere of our widest range of learning. 



This is a beautiful, lively, and active creature, common in some 

 places, scarce in others, and affording some room to conjecture that it 

 may be migratory. Certainly it is sometimes very difficult to be obtained, 

 nor ought the words of a distinguished Northern naturalist to be over- 

 looked, — " Hunc semel in mari vidi versus superficiem aquae, antennis 

 brachiisque longioribus mire ludificantem." — Fahricius, Fauna Groen- 

 landica. No. 219. 



The largest specimens in this country extend thirteen inches from 

 the tip of the antennae to the marginal extremity of the caudal fringe, 

 whereof the body, as invested by its shell or carapace, occupies six 

 inches to the point of the rostrum. The large claws, and the long an- 

 tennas, are of about half the extent of the whole animal, tliat is, be- 

 tween six and seven inches. 



First, the carapace or principal shell, commencing with the rostrum, 

 is guarded by five rows of spines ; three narrow indefinite segments, then 

 four strong and distinct ones, when the whole terminates with the 

 caudal segment, as composed of its five fringed members. 



It would be difficult to frame a minute desci*iption of the animal, 

 for which some general observations must suffice. The two claws com- 

 monly exhibit disparity in length and strength ; various rows of thorns 

 or teeth, all tipped with white, run longitudinally along the interior sur- 



