BIOLOGICAL SURVEY OF WOODS HOLE AND VICINITY. 



73 



sometimes happens that the species is recorded from an ahsolutdy qrcater number of 

 stations of another group than that for which it is here listed. Again, the caution must 

 be repeated (cf . p. 3 1 , 33) that in the field a specimen was frequently recorded from a cer- 

 tain type of bottom when it seems probable that the dredge, at the moment of taking it, 

 was passing over a quite different type of bottom. In many parts of our local sea floor 

 several distinct varieties of bottom may be encountered within a quite limited area. 



Nevertheless, we believe that real and important facts of ecology are revealed by 

 such tabulations as the foregoing, even though these may not in themselves present a 

 complete picture. For concrete illustrations of the assemblage of organisms which may 

 actually occur together on a given bottom, or at least within the area traversed during a 

 single dredge haul, the reader is referred to the tables on pages 58 to 62. 



Thus far the lists of "prevailing" species for one or another group of stations have 

 had no reference to the temperature factor. It has been thought desirable, however, to 

 present a list of those species which have been taken at one-fourth or more of the stations 

 within the cold-water area of the region, i. e., the area throughout which the water tem- 

 perature in summer has been found to be considerably lower than elsewhere. For this 

 purpose the Fish Hawk stations (and these only) were chosen, lying, in Vineyard Sound, 

 beyond (southwest of) a line drawn from Robinsons Hole to Kopeecon Point, and in 

 Buzzards Bay below a line drawn from Barneys Joy Point to Penikese Island. One 

 hundred and one stations were included in this area. 



IX. Species taken at otie-jourth (25) or more of the stations in the colder waters adjacent to 



the open ocean. 



Hydrozoa : 



Hydractinia echinata (34). 



Obelia geniculala (27). 



Halecium tialecinum (27). 

 Bryozoa: 



Crisia ebumea (43). 



;Etea anguina (25). 



Bugula turrita (70). 



Schizoporella unicornis (46). 



Cellepora americana (30). 

 Asteroidba: 



Asterias forbesi (51). 



Asterias vulgaris (58). 

 EcmNOiDEA: 



Arbacia punctulata (25). 



Echinarachnius parma (70). 

 Annulata: 



Harmothoe imbricata (39). 



Nereis pelagica (35). 



Diopatra cuprea (43). 

 Cirripedia: 



Balanus ebumeus (37). 

 Amphipoda: 



Unciola irrorata (27). 



Mginella longicornis (35). 



Isopoda: 



Idothea phosphorea (26). 

 Decapoda: 



Crago septemspinosus (49). 



Pagurus acadianus (39). 



Pagurus longicarpus (59). 



Libinia eraarginata (37). 



Cancer irroratus (75). 



Ovalipes ocellatus (41). 

 PelEcypoda: 



Anomia simplex (54). 



Pecteii magellanicus (26). 



Mytilus edulis (82). 



Modiolus modiolus (25). 



Area transversa (60). 



Nucula proxima (30). 



Venericardia borealis (63). 



Astarle undata (51). 



Astarte castanea (44). 



Crassinella mactracea (41). 



Cardium pinnulatum (55). 



Callocardia morrhuana (63). 



Ttllina tenera (55). 



Knsls directus (30). 



Spisula solidissima (72). 



