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 earried 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. 99. 
Hyalea, 2. 
Fig. 100. — Atlanta. 1. 
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 types 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. Salpæ, 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- 
