coe: nemerteans of west and northwest coasts. 289 



Nephridia remarkably limited in extent, but consist of unusually 

 large tubules situated above lateral nerves, 

 beside stomach, and immediately behind 

 brain. Two large canals often occur on each 

 side, one of which lies above and the other 

 below the slender intestinal caecum. After 

 a very short extent, they unite to form a 

 remarkably large efferent duct on each side, 

 which passes above lateral nerves to open on, 

 or immediately below, the lateral margin of 

 body. 



Cerebral sense organs voluminous and 

 highly specialized, situated immediately in 

 front of brain. 



Habitat. — This species has been collected 

 on piles of wharf at San Pedro, California, 

 and on kelp ' hold-fasts ' in 3-6 fms. outside 



same harbor, but is not common. Sexual products are mature in 

 August. 



Fig. 56. — Tetrastemma 

 su/nifer. Central sty- 

 lets and bases from two 

 individuals. 



76. Tetrastemma nigrifrons Coe. 



Harriman Alaska Expedition, 11, p. 159 ; PI. 1.5, fig. 7 ; PI. 16, figs. 

 6-9; PI. 17, fig. 1 ; PL 20, fig. 16; PI. 21, figs. 15-23, 1904. 



PL 2, fig. 26 ; PL 18, figs. 111-115 ; Text-figs. 57-59. 



Diffei'ent individuals of this species are of extremely varied colors 

 even when collected in the same locality, and present a number of 

 characters diverging from those of other described species of the 

 genus. The more important peculiarities of external appearance and 

 internal structure are as follows : — 



Body of moderate proportions, or rather slender for genus, 

 rounded throughout ; head more variable in size and shape than 

 in many related species ; provided with two pairs of lateral, oblique 

 furrows of more than ordinary distinctness, anterior pair lying 

 between anterior and posterior pairs of ocelli, and the posterior pair 

 situated just behind the posterior pair of ocelli, serving to mark off 

 the head from the body (PL 18, figs. 111-113). Each of the anterior 

 furrows extends on dorsal surface from lateral border obliquely 



