68 coE 



ramify more towards the ventral side of the esophagus. There is a sin- 

 gle pair of efferent ducts which are of enormous size as compared with 

 those of other species. These ducts are situated at about two-thirds the 

 distance towards the posterior ends of the nephridia, and open on the 

 dorso-lateral aspects of the body as usual. 



Habitat. — This species is common in mud and under stones in 

 muddy localities at Orca and Virgin Bay in Prince William Sound, 

 but was not met with elsewhere on the expedition. The individuals 

 are hardy and of sluggish movements. They do not break up nor 

 contract excessively when thrown into killing fluid, and the proboscis 

 is not usually everted when the animal is killed. Some, especially 

 the smaller ones, when preserved are nearly cylindrical, but most indi- 

 viduals are flattened ventrally. The color is fairly permanent in for- 

 malin, and even in alcohol for some months. 



Micrura Ehrenberg. 

 Symbolae Physicae, Berlin, 1831, 



This genus includes mostly moderately small, slender forms, gener- 

 ally less rounded posteriorly, and of rather more active habits than 

 Lineus. Its most marked distinction from the latter genus is that the 

 posterior extremity of the body is provided with a slender, usually 

 colorless, muscular caudal cirrus. This is formed of a continuation 

 of the muscular tissues and Integument beyond the posterior end of the 

 alimentary canal. 



The species of Micrura are generally, though not always, more 

 brightly colored and have more distinct markings than those of 

 Lineus. The vast majority of the species are provided with numerous 

 ocelli, though some are blind. The head is slender, and not distinctly 

 separated from the rest of the body. The lateral faces of the body are 

 not provided with thin edges as in Cerebratulus, the intestinal region 

 is not so much flattened, neurochord cells are not present in those 

 species which have been studied, and none of the species are able to 

 swim as do all species of Cerebratulus. The mouth is usually smaller 

 than in Cerebratulus^ and the intestinal lobes are not so deep. 



The proboscis is usually slender and comparatively weak ; the pro- 

 boscis sheath is sometimes considerably shorter than the body. 



25. MICRURA VERRILLI sp. nov. 

 p1. v, figs. I, 2, 3. 

 Body moderately elongated, widest anteriorly, tapering to an acute 

 anterior extremity ; much more slender posteriorly. Ventral surface 



