ALASKA NEMERTEANS 69 



flattened ; dorsal surface rounded. Head narrow in front. Cephalic 

 furrows long and deep ; at their posterior ends each is met by an ob- 

 lique, shallow depression above and below. Proboscis-pore exactly 

 terminal ; anterior ends of cephalic furrows well separated from pro- 

 boscis pore. Mouth small, situated as far back as posterior ends of 

 cephalic furrows. Caudal cirrus small, slender, easily broken off. 



Color. This is one of the handsomest and most striking of all the 

 described species of Nemerteans. The color of the dorsal surface is 

 deep purple or wine-color ; that of the ventral surface is purest white. 



On the dorsal surface are usually 15 to 40 very sharp, pure white, 

 transverse bands or lines connecting with the white color of the ven- 

 tral surface. These transverse bands are nearly as narrow as pencil 

 marks, and are situated at fairly regular intervals throughout the length 

 of the body. They are sometimes more or less interrupted, but 

 always sharp and distinct. On the dorsal surface of the tip of the 

 snout is a small triangular marking, always very conspicuous because 

 of its bright orange color. Following behind this is a narrow trans- 

 verse white band, followed by broad purple and narrow white bands 

 in succession. The cephalic furrows lie within the white color of the 

 ventral surface, and are bordered above with a very narrow margin of 

 white. They reach posteriorly as far as the second white band. 



After preservation in formalin or alcohol the worms are strongly 

 rounded below as well as above, and the color of the dorsal surface 

 changes from purple to red, while the orange spot on the tip of the 

 snout disappears. 



Ocelli. None were found. 



Proboscis. Colorless, and shorter than in many species of the 

 genus. Its microscopic structure shows distinctly the three muscular 

 layers and the muscular crosses characteristic of the family. The 

 inner circular muscular layer is very thin. The nervous plexus inside 

 the circular layer is usually well developed. 



Nervous system. The dorsal ganglion of the brain is divided poste- 

 riorly into two distinct lobes, of which the smaller, dorsal lobe ends 

 shortly, while the larger, ventral lobe continues into the cerebral sense 

 organ. Each of these sense organs is of about the same size as one of 

 the ventral ganglia, but considerably smaller than either dorsal ganglion. 

 The duct lying on the external border of each of the pair of cerebral 

 sense organs communicates, as usual, with the enlarged posterior end of 

 the cephalic furrow by means of a wide duct opening directly outwards. 

 The dorsal median nerve, lying just outside the circular muscular layer, 

 is remarkably conspicuous throughout the whole length of the body. 



