2OO COE 



about two-fifths the distance from snout to intestinal region, and is in 

 the immediate vicinity of the efferent nephridial ducts. The histo- 

 logical peculiarities of the various portions of the alimentary canal 

 have been described on previous pages for the two species mentioned 

 above. The change from stomach to intestine is gradual, and the true 

 intestinal pouches do not begin until after the appearance of a num- 

 ber of shallow pouches in the walls of the stomach. 



Blood and Nephridial Systems. The nephridia are very limited 

 in extent, being confined to the posterior half of the esophageal region 

 proper. Large nephridial tubules ramify among the esophageal blood 

 lacunae, and are collected into a main canal on each side. At the pos- 

 terior end of this canal a single efferent duct passes to the exterior 

 above the lateral nerves as usual. The nephridiopores are thus situ- 

 ated in the region where the esophagus opens into the stomach. The 

 proboscis sheath vessel leaves the rhynchocoel at the same place. 

 Here, too, the esophageal lacunae unite into a pair of ventro-lateral 

 vessels which pass back through the stomach region, and into which 

 the lateral vessels empty at the beginning of the intestinal region. In 

 the single specimen sectioned a pair of conspicuous longitudinal folds 

 appear in the stomach epithelium immediately internal to the ventro- 

 lateral vessels, and in many places the vessels themselves are situated 

 within these folds. 



Nervous System. Brain and principal nerves as in related species. 

 The median dorsal nerve is remarkably conspicuous throughout the 

 length of the body. The internal median nerve, which rests on the 

 dorsal side of the proboscis sheath, is also conspicuous. It is best de- 

 veloped in the stomach region. 



Cerebral sense organs present no peculiarities. 



Reproductive Organs. Sexual products were not developed in 

 individuals collected in August, and had evidently been discharged 

 some time previously. 



Habitat. Among * hold-fasts' of kelp and other algae, low water 

 to 2 fms., Dead Man's Island, San Pedro, Calif., not common; on 

 floating kelp 'hold-fasts' off San Pedro Harbor, one specimen. 



23. CEREBRATULUS ALBIFRONS Coe 



pi. xvn, fig. 9. 



Proc. Wash. Acad. Sci., in, p. 82 ; pi. iv, figs. 3, 4, 1901 ; also preceding 

 article, which has identical paging. 



Specimens collected in mud in San Pedro Harbor, California, 

 measured upward of 30 cm. in length. Similar specimens were 



