306 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



sometimes with white longitudinal stripe. Variety bicolor (b) has broad 

 quadrangular cephalic marking and brown body with white longitudinal 

 stripe. Variety zonatum (c) is deep brown or reddish brown with from 

 12 to 20 transversely elongated white spots. Variety purpuratu?n {e) \s 

 dark reddish brown or purple. There are many intergrading individuals 

 with combinations of these patterns and other variations. 



Habitat. Common among algae, bryozoa, and other growths on rocks 

 and piers between tidemarks and below; often found on kelp holdfasts. 



Distribution. Previously known from Puget Sound and southward 

 to the coast of Mexico. Collected by the Allan Hancock Expedition of 

 1935 at Salinas Bay, Costa Rica. 



89. Tetrastemma quadrilineatum Coe, 1904 



T. quadrilineatum Coe, 1905, 1905a. 



Habitat. Among algae, ascidians, and other growths on rocks and 

 piers near low-water mark and in tide pools. 



Distribution. At present known only from Monterey Bay, California, 

 to Ensenada, Mexico. 



90. Tetrastemma reticulatum Coe, 1904 



T. (Oerstedia) reticulatum Coe, 1904, 1905. 



Habitat. Among algae and other growths on spiles and rocks near 

 low-water mark. 



Distribution. At present known only from San Pedro and San 

 Diego, California. 



91. Tetrastemma sexHneatum, new species 

 (Plate 24, figs. 5, 6) 



Individuals of this species resemble those of T. quadrilineatum in 

 general appearance but differ in having 6 longitudinal dark stripes. 



Body. Rounded ; rather short and stout. 



Size. Minute; the single specimen available for study was a fully ripe 

 female which measured only 5 mm in length and 0.5 mm in diameter. 



Color. General color gray or slightly yellowish, conspicuously marked 

 with 6 longitudinal stripes of dark brown pigment. Of these, 4 are 

 symmetrically placed on dorsal surface of body and one on each lateral 

 margin or slightly ventral to margin (Figs. 5, 6). Pair nearest to median 



