212 PLATHELMINTHES 



Key to the genera of Tetrastemmidae: 



Oi Marine animals. 



&! Body rather flat, soft in appearance 1. TETRASTEMMA 



6 2 Body cylindrical, rigid in appearance 3. OEBSTEDIA 



a 2 Fresh-water animals 2. STICHOSTEMMA 



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

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

 cephalic gland large; mestly unisexual, occasionally hermaphroditic: over 

 60 species. 



Key to the species of Tetrastemmidae here described: 



a t Body slender. 



61 Body widest at forward end, tapering to hinder end. 



d Body whitish T. CANDIDUM 



c 2 Body more or less spotted T. VEBMICULUM 



6 2 Body widest in the middle and tapering both ways T. ELEGANS 



c 2 Body rather stout with dorsal stripes T. VITTATUM 



T. candidum (0. F. Miiller) (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 ways; back with a median yellow and 2 lat- 

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

 grass and on stones in Long Island and Vineyard Sounds. 

 T. vermiculum (Quatrefages). Body slender, pale yel- 

 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 

 Fig! 341 Island and Vineyard Sounds; Europe. 



T candldum a T. vittatum (Verrill). Body rather stout, green or 



(Verrii). 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; excretory 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 very transparent, with 6, rarely 4 or 

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

 Pennsylvania and Connecticut; eastern United States. 



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

 Vol. 35, 1901, 



