294 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 2 



Genus PROSORHOGHMUS Keferstein 



Only one species of this genus is known from the region covered by 

 this report. 



60. Prosorhochmus albidus (Coe), 1905 

 (Plate 25, fig. 20) 



Tetrastemma albidum Coe, 1905. 



Habitat. Among algae, particularly corallines, and other growths on 

 rocks and spiles exposed to the surf. 



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

 and southward to Ensenada, Mexico. Common in many localities. 



Reproduction. Usually oviparous, occasionally viviparous (Fig. 20), 

 because of retention of fertilized eggs within one or more of the ovaries. 



Genus OERSTEDIA Quatrefages 

 Only a single species of this genus has been found on the Pacific coast. 



61. Oerstedia dorsalis (Abildgaard) 



Tetrastemma dorsalis Mcintosh, 1873; Verrill, 1892; Oerstedia dorsalis 

 Burger, 1895; Tetrastemma (Oerstedia) dorsale Coe, 1904, 

 1905 ; Oerstedia dorsalis Stiasny-Wijnhoff, 1930. 

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

 low-water mark and below. 



Distribution. Widely distributed in Northern Hemisphere; northern 

 coasts of Europe to Madeira; Nova Scotia to southern New England and 

 southward ; Puget Sound, Monterey Bay, California, and southward to 

 Ensenada, Mexico. 



Family Amphiporidae 



Two genera found on the Pacific coast are members of this family. 



Key TO Genera 



1. Ocelli extend posteriorly along lateral nerve cords beyond brain ; 

 basis of central stylet cylindrical and sharply truncated or con- 

 cave at posterior end Zygonemertes 



1. Ocelli do not extend posteriorly beyond brain; basis of central 

 stylet truncate conical or pear shaped and usually rounded at 

 posterior end Amphiporus 



