﻿394 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



spire anchored posteriorly; no contractile vessel. Length of a typical 

 fully relaxed specimen 140 mm.; anus (about in middle of trunk 

 proper) to posterior end 1.3 mm.; diameter of trunk 1.5 mm.; of 

 introvert 0.75 to 1 mm ; introvert 6 to 8 times length of trunk. 



Description. — The bod}^ wall is thin, usually translucent, a bleached 

 brown or yellow. The trunk is short, slender, and fusiform; the in- 

 trovert is extremely long and filiform. At maximum retraction it 

 entirely fills the body cavity with irregular coils, displacing the 

 viscera. The introvert cannot be retracted as far as the nephridio- 

 pores or the anus, which is at about the middle of the trunlv and 

 posterior to nephridiopores. There is no sharp distinction between 

 the trunk and the introvert. The posterior end of the bodj^ which 

 is often pointed, is thickly beset with short ovoid or cylindrical brown 

 papillae, against a paler skin, 0.025 to 0.035 mm. in height and thick- 

 ness. Overlapping the papilla zone and extending far along the in- 

 trovert are much larger, transversely elliptical, pale brown glands, 

 producing low conical eminences with a subcentral darker pore. 

 They measure 0.28 by 0.1 mm. on the trunk and become somewhat 

 smaller on the introvert, where they form a few not very regular 

 longiseries. In specimens from Monterey Bay these glands are more 

 conspicuous than in southern examples. Wlien the specimen is well 

 relaxed and fixed, the glands are low conical with pointed apex and 

 darker than the general sldn, even on the introvert, where they also 

 are alined as more prominent parts of successive ring welts. The 

 skin, in addition, is marked by numerous fine transverse fiu-rows and 

 at the posterior end of the trunk by longitudinal ones. 



Only two jMonterey specimens are well enough expanded to show 

 the head region. The tentacular crown is very small, about 0.25 mm. 

 in diameter, in one specimen surrounded by a collar but not in the 

 second. The exact number of short filiform tentacles cannot be de- 

 termined, but it is between 12 and 20 (pi. 24, fig. 4). A short dis- 

 tance back of the tentacles is a zone of tiny hooks. They form 20 

 to 50 very regular rings, are close together, and unless the skin is 

 taut they lie in furrows separated hj ridges. The hooks average 

 0.02 mm. in height, are curved, and on the posterior margin near the 

 base there is a comb of slightly curved thorns. This hook zone oc- 

 cupies only 3 mm. of the very long introvert and is therefore visible 

 only in fully extended specimens. 



There are four retractor muscles (not two only as Chamberlin 

 states). They are small and originate on about the same level as 

 the anus, the dorsals as far as possible in front of the ventrals. As 

 shown (pi. 24, fig. 2), they soon unite into a solid muscidar column, 

 which proceeds to the head. Along the dorsal side of this, and se- 

 curely fastened to it, runs the esophagus. There is only a short seg- 

 ment between the end of the esophagus and the beginning of the in- 



