212 



PL A THELMINTHES 



Key to the genera of Tetrastemmidae: 



ttj Marino animals. 



61 Body rather flat, soft in appearance 1. Tetkastemma 



62 Body cylindrical, rigid in appearance 3. Oerstedia 



Cj Fresh-water animals 2. Sticiiostemma 



1. Teteastemma Ehrenberg. Body small, with the 4 eyes forming 

 a rectangle; occasionally each eye is double or represented by a group; 

 cephalic gland large; mostly unisexual, occasionally hermaphroditic: over 

 60 species. 



Key to the species of Tetrastemmidae here described: 



fli Body slender. 



6i Body widest at forward end, tapering to hinder end. 



Ci Body whitish T. candidum 



d Body more or less spotted T. vermiculum 



62 Body widest in the middle and tapering both ways T. elegans 



02 Body rather stout with dorsal stripes T. vittatum 



T. candidum (0. F. Mliller) (Fig. 341). Body very contractile and 

 slender, white, light green, or yellowish in color, 2 cm. long and .5 mm. 

 wide; head wide; hinder end tapering: common between 

 tide lines and beyond, among algae, from Long Island 

 Sound to Bay of Fundy; Europe. 



T. elegans (Girard). Body slender, tapering from the 

 middle both w^ays; back with a median yellow and 2 lat- 

 eral brown stripes, 2 em. long, 1 mm. wide : among eel 

 grass and on stones in Long Island and Vineyard Sounds. 

 T. vermiculum (Quatrefages). Body slender, pale j^el- 

 low or reddish in color and more or less spotted ; forward 

 end broader than the hinder, 2 cm. long, 1 mm. wide: 

 common on muddy bottoms between tide lines in Long 

 Island and Vineyard Sounds; Europe. 



T. vittatum (Verrill). Body rather stout, gi-een or 

 yellowish in color, sometimes with 1 or 2 dorsal stripes, 

 5 cm, long, 4 mm. wide: common on muddy bottoms at low-water mark 

 and beyond in Long Island and Vineyard Sounds. 



2. Stichostemma* Montgomery. Similar to Tetrastemma but with 



3 pairs of eyes; excretoiy organs extending the length of the body: 7 

 species, in fresh water. 



S. rubrum (Leidy) (^S*. asensoriatum Mont.). Body slender, 18 mm. 

 long, yellow or reddish in color and veiy transparent, with 6, rarely 4 or 

 8, eyes; preoral sense pit wanting; cephalic gland weak; hemaphroditie : 

 Pennsylvania and Connecticut; eastern United States. 



Fig. ,341 



Tetrastemma 



candidum 



(Verrill). 



* "The Habits and Natural History of Stichostemma," by C. M. Child, Am. Nat., 

 Vol. 35, 1901. 



