250 bulletin: museum of comparative zoology. 



Ocelli. — Usually 6 to 12 ocelli on each side of head, arranged in 

 two groups on each side as in A. imjmrispinosus, exce])t that the 

 anterior ends of posterior groups often appear to lie externally to 

 posterior ends of anterior groups. Each of the four groups has 

 about the same number of ocelli (PI. 16, fig. 93 ; PI. 22, fig. 152). 



Proboscis. — Proboscis sheath extends very nearly to end of 

 body and contains numerous flattened, colorless corpuscles. Pro- 

 boscis attached to wall of sheath a little posterior to middle of body 

 by means of root-hke fibers. Provided with slender central stylet 

 and two pouches each containing 1, 2 or 3 similar accessory stylets. 

 Basis of central stylet slender, a little more than twice as long as 

 wide, and usually a trifle shorter than the stylet itself. Measure- 

 ments of several bases and stylets give a length of basis from .035 

 to .063 mm., with a width of .017 to .027 mm., while stylet itself is 

 commonly .036 to .075 mm. in length, and acutely pointed (PI. 16, 

 fig. 94; PL 22, fig. 153). There are 10 proboscidial nerves. 



Brain large, ])ale in color ; cerebral sense orga)ts are about two 

 thirds the diameter of dorsal ganglia, and are situated a little more 

 than half way from tip of snout to brain. 



Habitat. — jVConterey, California, on piles ; Pacific Grove, among 

 corallines. 



This minute species is common in the localities mentioned, as is 

 also A. im2:>arispinosus, with which it is associated, and the young 

 individuals of which it very closely resembles. It can hardly be 

 distinguished without examination of proboscis, which always con- 

 tains but two pouches of accessory stylets, while that of A. impari- 

 spinosus has three even when young. The number of proboscidial 

 nerves is also very different in the two species. 



60. Amphiporus formidabilis Griflin. 

 Ann. New York Acad. Sci., 11, p. 211, 1898. 



Atnphiporus exilis Coe, Proc. Wash. Acad. Sci., 3, p. 54, PI. 3, fig. 

 1; PI. 8, fig. 5; PL 11, fig. 3, 1901 ; Harriman Alaska Expedi- 

 tion, 11, p. 54, 1904. 



PL 17, figs. 101, 102; Text-figs. 13, 15, 23, 54. 



This very common and widely distril)uted species may be recog- 

 nized by the following characters : — Body remarkably slender for 



