1897.] NEW YORK ACADEMY OF SCIBXCES. 161 



getber as messmates, may be explained by (1) a wide distribution 

 of these commensalists in geological time ; (2) the cosmopolitan 

 occurrence of one and the extension of the other; (3) extension 

 or migration of both from a common center. This interesting 

 problem must be postponed until several careful comparisons of 

 tlie respective repi'esentatives of New and Old World tj'pes have 

 been made but it seems probable that instances of littoral com- 

 mensal forms from widely separated areas cannot be explained 

 by long larval periods and ocean currents. Finally, that com- 

 mensal habits may be parallel evolutions, would seem to be indi- 

 cated by the very important differences between the two genera 

 of the family Entoconchidre In their larval development, cer- 

 tain apparently adult morphological characters indicate diffierent 

 genetic relationships, and that different families of mollusca 

 have become endopai-asitic in holothurians. Even here, however, 

 extremely different life habits in the host may have affected the 

 early stages of the mollusk. 



In this place ma}'^ be mentioned Semper's* close comparison 

 of the Philippine fauna with that of the Mediterranean, and his 

 explanation of this fact as lying in the ocean current which 

 sweeps eastward. The same current is carried on to the Pacific 

 coast of North America. Although not as yet able to offer ex- 

 tensive evidence, the majority of species so far determined of 

 nemerteans, holothurians mollusca and annelids approximate 

 more nearly European than Eastern United States boreal species. 



Among other instances of commensalism observed in the 

 Puget sound district may be mentioned a yellow and black 

 striped Nereis in the parchment-like tubes of Chsetopterus, a 

 Lepidonotus-Wke form in Serpula tubes, Halyosydnia with Fis- 

 surella (Neah Bay) and an annelid of unknown relationships 

 living on a small Teleost. At Neah Bay the scaly annelid 

 wh'ch is commonly found on Holothuria californica Stimpson 

 was also observed on Dermaster of shallower water. 



Sternapsis fossor (?), Pectinaria, Ampharete and a white den- 

 drochirotid holothurian were taken in Sequim Bay from a depth 

 of ten to fifteen fathoms of water. 



Discovery Bay and Port Townsend Harbors. 



The conditions in these two harbors are largely identical — 

 sandy bottoms along the southeastern shores, washed by strong 

 tides and currents. The particular interest centering in Dis- 

 covery Bay is the fact that it is the spawning ground of 

 Hydrolagus colliei. Eighty empty egg cases were taken in a 



* Animal Life. Ciiapter IX. 



Transactions N. Y. Acad. Sci., Vol. XVI, Sig. 11, April 13, 1897. 



