496 PROCEEDIXCtS of the national museum vol.84 



tion 4302, "blue mud" (^1. campyleca). The bottom record for station 

 4777 reads "fine gravel", yet a small colony of Allopora verrilli and 

 two of Errinopora nanneca (also three species of encrusting bryozoans) 

 were growing on a very hard pebble 50 by 30 by 25 mm. Rocks, 

 pebbles, and shells form the usual foundation whether or not there be 

 mud, sand, or fine gravel accompanying. Allopora campyleca favors 

 black sand or blue mud; while Allopora boreopacifica is found on 

 pebbles in broN\Ti mud and fine black sand. 



As regards temperature, the lowest is favored by Allopora boreo- 

 pacifica, A. norvegica pacifica, and Errinopora stylifera at 29.8° to 32° 

 F. Then there is a hiatus. From 37° (the probable temperature at 

 station 3480) to 39° are found Stylaster cancellatus, S. elassotomus, 

 S. gemma.scens alaskanus, Allopora campyleca (and its subspecies tylota 

 and trachystoma) , A. polyorchis, A. moseleyana (and forma leptostyla), 

 A. stejnegen, A. brochi, A. verrilli (typical), Cryptohelia frophostega, 

 Errinopora nanneca, E. zarhyncha, and Distichopora borealis. Between 

 41° and 44° is found A. campyleca not precisely typical nor yet well 

 enough differentiated to show tangible characters. It is probable 

 that A. papulosa, A. verrilli, and A. petrograpta occur here. Between 

 46° and 52° are foimd A. campyleca paragea, A. venusta, A. californica, 

 A. porphyra, Errinopora pourtalesii, and at the lower limit A. petro- 

 grapta. E. pourtalesii ranges from the Strait of Georgia to south of 

 Monterey Bay, and A. californica from the Farallone Islands to 

 Lower California. Both species probably range into water warmer 

 than 52°. 



It is evident that station 3480 is a very favorable environment for 

 hydrocorals, since there was dredged here a considerable bulk of ma- 

 terial, comprising eight forms, some of which are massive. This sta- 

 tion was in Amukta Pass, east of the Andreanof Islands of the Aleutian 

 Chain, in 283 fathoms, rocky bottom with black sand. The Aleutian 

 Islands form the crest of a very long, curved, mostly submarine 

 raountain chain, which falls away to great depths on the south. It 

 constitutes a partial barrier athwart Bering Sea, one of the sources of 

 cold bottom water of the north Pacific. That bottom currents are 

 present in the numerous passes of the Aleutian Chain is inevitable. 

 Such water should be rich in oxygen and in planktonic organisms, or 

 their dead remains. 



The structure of the corallum of some Stylasters and Alloporas 

 indicates that the species live where there is a gentle current predomi- 

 nantly in one direction. The peripheral branches are bent slightly 

 toward the anterior face of the colony, which becomes slightly con- 

 cave. Most of the gastrozooids are on the front and sides of branches, 

 or on the sides only. Usually the back, presumably facing the cur- 

 rent, is almost devoid of gastrozooids. This form of growth is also 

 found in some species of Cryptohelia. The Alloporas of station 3480 



