COE: NEMEETEANS OF WEST AND NORTHWEST COASTS. 161 



and fully described by Miss Thompson (: 02) may be recognized by 

 the following characters : — 



Body rather slender, usually 5-8 cm. in length, rather translu- 

 cent. Head slender, when extended tapering to a fine point ; with- 

 out cephalic furrows (Text-lig. 18), pure white in color. Esophageal 

 region rounded ; wdiite, very pale yellowish or flesh color. Intes- 

 tinal region flattened in life, but rounded after preservation ; color 

 varies from rose to pale yellow, light brown or chocolate brown, 

 being largely dependent on the amount and character of the con- 

 tents of alimentary canal. Posterior extremity provided with a 

 conspicuous, although slender, white caudal cirrus (Text-lig. 4). 



In internal organization, the presence of an internal circular 

 muscle at the beginning of intestinal region, the division of the 

 anterior portion of alimentary canal into esophagus proper and 

 stomach, the opening of the ciliated canals leading to cerebral 

 sense organs into shallow lateral pits on margins of head in place 

 of cephalic furrows, the absence of any retractor muscle of pro- 

 boscis, and the absence of the inner longitudinal muscle of pro- 

 boscis are among the more important peculiarities of the species. 



Habitat.— Common on the sand flats laid bare by the lowest 

 tides in San Pedro Harbor, California. The species is here asso- 

 ciated with several other forms to which it shows a general super- 

 ficial resemblance. These are Carinella peUacida, Carinomella 

 lactea, Carinoma mutabilis^ and immature individuals of Micrura 

 griffini. The sharj^ly pointed white head, without lateral furrows, 

 and the conspicuous white caudal cirrus, however, will serve to dis- 

 tinguish Zygeupolia from any of these other forms. 



Lineus Sowerby. 

 The British Miscellany, London, p. 15, 1806. 



Representatives of this genus are characterized by slender, 

 sometimes thread-like bodies, usually rounded throughout. The 

 body is commonly twisted and coiled into an irregular mass. The 

 movements are sluggish. The animals creep over objects and 

 readily move about on the surface of the water, biit they are 

 unable to swim. The body is extremely contractile ; the head is 

 often slightly wider than the body, of oval shape, and is usually^ 



