﻿416 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 102 



vessel; nephridia shorter; alimentary canal much longer, the spu-e 

 consisting of upward of 100 coils. 



Description — This is a larger species, adult specimens from the 

 type locality being 150 to 260 mm. long, while one from Tomales 

 Bay measures 320 mm. and must have been considerably longer 

 when living. The body is very slender, cylindrical, tapering very 

 gradually to the rounded or bluntly pointed posterior end. The 

 greatest width of fully extended living specimens is one-twelfth to 

 one-twenty-fifth the total length — usually nearer one-twentieth. 

 The introvert is cylindrical, its length about one-sixth to one-seventh 

 the total length; the anterior fifth of the introvert is a glossy brown 

 collar or zone, marked by fine creases. This collar is followed by a 

 smooth, not so broad whitish zone. Back of this the skin is pale 

 sepia thickly peppered with tiny dark-brown papillae, which are more 

 numerous than in Dendrostomum zostericolum, especially anteriorly 

 (pi. 27, fig. 3, a). Posterior to the anus these are replaced by strongly 

 convex brown glands or low protuberances, generally of three sizes, 

 from 0.04 to 0.1 mm. diameter. When the skin is stretched, very 

 small, inconspicuous subquadrate areas can be discerned, with one of 

 these glands to an area. The tentacles are similar to those of zoster- 

 icolum,, bush}^ in large specimens, and one or both of the dorsal tentacles 

 are smaller than the others. In the very large Tomales Bay animal, 

 with well-expanded tentacles, both dorsals are conspicuously smaller 

 than the others. The nuchal organ is broader than long, the surface 

 is furrowed and the anterior margin is hidden by a broad crescentic 

 sht. 



The longitudinal muscle layer is satiny smooth and the oblique 

 bands of muscle between it and the chcular layer are more con- 

 spicuous than in large examples of D. zostericolum. The two large 

 retractors are impressively long and have their origin at the beginning 

 of the posterior fifth of the body. The line of attachment is either 

 concave or straight. The spindle muscle is attached as in zostericolum, 

 but is longer in accordance with the greatly lengthened intestine. 

 Fixing muscle F^ seems not to be always present and F^ and F^ are 

 absent. 



Perhaps the most conspicuous difference between the two species is 

 the much longer intestine of D. perimeces. In a specimen that is by 

 no means the largest, there are about 100 single coils in the spiral, 

 while in D. zostericolum there are less than half as many. 



The contractile vessel terminally has sLx to nine blind tubules. 

 Branches from the collateral vessels pass along the ventral side of the 

 esophagus and sometimes anastomose, but do not form a network. 



The nephridia are similar to those of D. zostericolum but allowing for 

 variation are definitely shorter than in that species. The nephrostome 

 opens directly forward. 



