184 SHELLS AND MOLLUSCOUS ANIMALS. 



to them all. Our figure represents the starry 

 botryllus (Botryllus stellaris), of its natural size, and 

 a magnified single group. Other families of the 



Ascidise move through the waters, linked in chains, 

 giving out their lights in the darkness; and to 

 this tribe belongs the wondrous Pyrosoma, whose 



greenish phosphorescent light gleams at night from 

 its living shoals, upwards of a m: 



mile in breadth, and 



as the vessel dashes among them, illumines the sea 

 with gleams of light. 



Interesting and wonderful as are some of the 

 shell-less mollusks, yet the forms which are found 

 in greatest number and variety are enclosed in 

 their beautiful ornamental coverings. The bivalve 

 mollusca compose the class termed Conchifera. 

 Our shores are strewed with multitudes of the 

 common kinds ; our limestone rocks and chalky 

 cliffs are full of the double valves of animals of 

 past ages. The dredge brings up many of those, 

 which we know must be lying in countless myriads 

 in the deep sea. Gaze into the rocky pools among 

 the crags, and we see them among the thousands 

 of living creatures revelling there; and, perhaps, 

 no spot exhibits in so small a space so many 

 individual and varied forms of life. The large 

 sea-weeds have, tangling about their fibres, or 



