THE PELAGIC FAUNA AND FLORA. 



187 



pouches, bag-like expansions of the lower floor of the bell, which 

 hang down into the bell cavity. Among the more interesting 

 hydroids may also be mentioned a species of Glossocodon (Fig. 

 94), noticeable for the changes it undergoes during growth. 

 (Figs. 95, 96.) 



Of the surface mollusks of the Gulf Stream, Janthina (Fig. 

 97) is very common, and is often seen in large numbers, 

 helplessly carried along by the current with the dark blue 

 Glaucus. (Fig. 98.) During the day an occasional pteropod 

 is seen ; but at night no cast of the tow-net is made without 



Fig-, m. 



Hvalea. f 



Fiff. 100. — Atlanta. V°- 



bringing them up in numbers. Characteristic of the Gulf 

 Stream are Hyalea (Fig. 99), which, like the more common 

 Atlanta (Fig. 100), Styliola (Fig. 101), Pleuropus (Fig. 102), 

 and Tiedemannia (Fig. 103), find their way far north to the 

 shores of Narragansett Bay and southern New England ; while 

 among the more common tvpes of the Straits of Florida and 

 of the Gulf of Mexico are" Salpa, Doliolum (Figs. 104-106), 

 Pyrosoma (Fig. 107), and Appendicularia (Figs. 108, 109), 

 all belonging to types of which individuals collect frequently 

 in such numbers as to fill the ocean as far as the eye can 

 penetrate, reaching out for miles in all directions. Salpae, as 

 has been shown by Moseley, sink rapidly to the bottom (two 

 thousand fathoms in two days) where they die ; and their dead 

 bodies, as well as the mass of dead pteropods, heteropods, crus- 



