NO. 13 COE: REVISION OF THE NEMERTEAN FAUNA 289 



are approximately 0.027 mm in diameter and the statoliths about 0.012 

 mm. The statolith usually lies somewhat excentrically in the statocyst 

 and toward the median line of the body, but the position changes when 

 the brain is compressed. 



Proboscis. Sheath limited to anterior fourth of body. Proboscis very 

 slender, with long slender canal in place of the usual bulblike middle 

 chamber; posterior chamber remarkably long, with thick glandular walls; 

 with slender retractor at end; armature minute; central stylet very 

 slender, slightly longer than the slender cylindrical basis. In sexually 

 mature individuals the basis is only about 0.03 mm in length and 0.006 

 mm in diameter. The length is thus about 5 times as great as the width. 

 The central stylet is about 0.04 mm long. There are 2-4 accessory 

 stylets in each of the 2 lateral pouches. Both central and accessory stylets 

 have spiral ridges, giving them a braided appearance because of their 

 transparency (Fig. 41). 



Cephalic glands. Voluminous, extending back of brain into foregut 

 region. 



Cerebral sense organs. Small, situated near anterolateral border of 

 brain. 



Lateral sense organs. A pair of remarkable sense organs extends 

 throughout most of the foregut region on the lateral margins of body in 

 close proximity to the nerve cords. The sensory cells of each sense organ 

 are situated in a longitudinal groove at the base of the surface epithelium 

 and are innervated by an almost continuous row of fibers from the 

 adjacent nerve cord. 



Reproduction. Sexes separate; gonads situated laterally, not alter- 

 nating regularly with intestinal diverticula; spermaries are several times 

 more numerous than ovaries. Sexually mature in spring and summer in 

 southern California. 



Habitat. In sand underlying corallines and other growths on rocks 

 and in tide pools on the open coast ; locally common. 



Distribution. At present known only from San Diego, Califox-nia. 



Family Prosorhochmidae 

 Key TO Genera 



1. Body slender; cerebral sense organs beneath or behind ocelli; 



intestinal diverticula mainly dorsal to intestine . Prosorhochmus 

 1. Body not very slender; cerebral sense organs anterior to ocelli; 



intestinal diverticula mainly lateral to intestine . . . Oerstedia 



