EXDEMISM IN THE NORTH PACIFIC 43 



The list of endemic species is far more considerable and comprises, 

 for California alone, more than 500 species. Fewer than two per cent 

 of the total number are cosmopolitan. 



Descriptions of some new and little known species follow. 



CIRRATULIDAE 



Members of this family have been conspicuously abundant in samples 

 from the San Pedro Basin, California. Especially abundant in depths to 

 300 fathoms are representatives of seven genera: Tharyx Webster and 

 Benedict, Chaetozone Malmgren, Caulleriella Chamberlin, Acrocirrus 

 Grube, Cirratulus Savigny, Cirriformia Hartman, and Cossura Webster 

 and Benedict. Species of three to five genera may occur together in an 

 area covering not more than three square feet of surface. This is especially 

 so for species of Tharyx, Chaetozone, Caulleriella, Cossura, and Cirra- 

 tulus. Most often present, but seldom in great numbers, is a species of 

 Cossura, described below. 



Cossura Webster and Benedict, 1887 



Type C. longocirrata Webster and Benedict 



The body is long, cylindrical, and tapers to both extremities ; it con- 

 sists of many segments. It resembles smaller cirratulids, except that there 

 are no paired lateral filaments or branchiae. A single long tentacle is 

 inserted middorsally on one of the anterior segments. Parapodia are 

 biramous ; each is a short, papillar mound or ridge from which the simple, 

 distally pointed setae project in fan-shaped series. Setae are essentially 

 of one kind and emerge in alternating double rows. The prostomium is 

 a simple rounded or subconical lobe, either with or without a pair of 

 simple eyespots at the sides. The first one or two visible segments are 

 apodous. 



Cossura is unlike typical cirratulids and may have more direct 

 affinities with members of the subfamily CTENODRILINAE Monti- 

 celli, especially w^ith the genera Raphidrilus Monticelli and Zeppelinia 

 Vaillant (see Fauvel, 1927, pp. 109-110) which also have a single 

 median antenna and simple pointed setae. 



A single species, C. longocirrata Webster and Benedict, has been 

 attributed to the genus. It was first described from Eastport, Maine, in 



