THE PYBOSOME8. 149 



first discovered and established the genus, ' we experienced one 

 of the strongest of the short-lived storms peculiar to the region 

 of calms in the Atlantic. The sky was on all sides loaded with 

 heavy clouds ; all around the obscurity was profound ; the wind 

 blew violently, and the ship cut her way with rapidity. Suddenly 

 we discovered at some distance a great phosphorescent band 

 stretched across the waves, and occupying an immense tract in 

 advance of the ship. Heightened by the surrounding circum- 

 stances, the effect of this spectacle was romantic, imposing, sub- 

 lime; ri vetting the attention of all on board. Soon we reached the 

 illuminated tract, and perceived that the prodigious brightness 

 was certainly and only attributable to the presence of an innumer- 

 able multitude of largish animals floating with the waves. From 

 their swimming at different depths, they took apparently different 

 forms ; those at the greatest depth were very indefinite, presenting 

 much the appearance of great masses of fire, or rather of enormous 

 reddish cannon-balls ; whilst those more distinctly seen near the 

 surface perfectly resembled incandescent cylinders of iron.' 



The Conchifera, or the molluscs contained within a bivalve 

 shell, comprise the two groups or orders of the Brachiopoda and 

 the lamellibranchiate bivalves. The former, which are chiefly 

 fossil, occur only in a few genera in the present seas, and are 

 characterised by the two long fleshy ciliated and spiral arms 

 which they use for opening their shell. Their mantle is 

 organised so as to be serviceable for respiration, and the numer- 

 ous cilia with which their arms are covered produce the cur- 

 rents that both provide them with food and aerate their blood. 

 They generally live in the deeper seas,, either attached to other 

 bodies by a sinewy stalk proceeding from an orifice at their 

 apex, or fixed, like the oyster, by their shells. 



The lamellibranchiate bivalves, which are spread in several 

 thousand species over all the seas from the poles to the equator, 

 play a far more important part than the brachiopods in the 

 present economy of nature. Every flood casts their empty shells 

 upon all the coasts of the ocean, and their shattered valves. are 

 almost as numerous as the sands which line its shores. Their 

 forms and their colours are as various as their modes of life, but 

 their structure is in every case exactly suited to their wants. 



Those which, enjoying a free life, are capable of wandering 

 from place to place, or at least of changing their position, 



