342 Dr. W. C. M'Intosh on the 



abdomen ; the importance, therefore, of ascertaining by close 

 inspection whether the line and the viscid fluid in which it is 

 enveloped proceed from the same spinning-tube or not will be 

 immediately apparent. It is evident, from the materials of 

 which they are composed possessing such widely different pro- 

 perties, that they cannot be produced by the same organ of 

 secretion. 



There is a difficulty also in comprehending how a cylindrical 

 body of viscid fluid can be resolved by molecular atti-action 

 into a series of large and small globules disposed on the line 

 alternately at minute and most regular distances from one 

 another. 



Had Mr. Beck been spared to continue his researches, he 

 might perhaps have been enabled, by his well-known skill as 

 a microscopist and by the advantage he possessed in having 

 superior optical instruments at his command, to throw some 

 light on the obscure phenomena here submitted to the consi- 

 deration of arachnologists, which remain as problems yet 

 waiting a solution. 



XLVIII. — On the Invertebrate Marine Fauna and Fishes of 

 St. Andreios. By W. C. M'Intosh. 



[Continued from p. 815. J 



Section II. MOLLUSC A (proper). 



The Mollusca are chiefly procured by dredging, examina- 

 tion between tide-marks, or the deep-sea lines of the fisher- 

 men, though certain storms sometimes strew the sands with 

 many species in great profusion. Not a few of the rarer forms 

 are found in the stomachs of fishes, such as the cod, haddock, 

 and flounder. The remarks on the class may be arranged in 

 three divisions, founded on the economical value, peculiar 

 habits, and rarity. 



By far the most important species in the first group is the 

 common mussel {My tilus ednlis) , which, occurs in vast numbers 

 in the form of mussel-" beds " on muddy flats, chiefly situated 

 on the right bank of the estuary of the river Eden. Attached 

 to stones, sticks, and to each other, these shell-fish luxuriate 

 in abundance of Diatomaceae, Infusoria, and other minute 

 forms of animal and vegetable life. From their special value 

 as bait the city derives a considerable annual revenue ; and if 

 the wise protection only lately enforced were supplemented by 



