274 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 



they are, like the Opheliida3, less characteristic of the localities to 

 which they belong than the Maldanidse and especially the Amphareti- 

 die, whose large tubes, built of mud, and sometimes associated with 

 those of the Eunicidae, must, judging from the masses in which they 

 are found, be a marked feature of certain localities. 



It interested me especially to find that the Serpulidse also descend 

 to great depths (860 fathoms) in this region of the sea, because, in 

 working up the Annelids collected by the " Porcupine " Expedition, I 

 had noticed the absence of the Serpulidas at great depths, and left it 

 undecided whether these forms were excluded, as they seem to have 

 been, by the peculiar nature of the bottom or by the low temperature 

 of the deep-sea water. The Serpula now lying before me, from a 

 depth of 310 fathoms (Station No. 19), is full grown; in its locality 

 the sea bottom, of the constitution of which I have no other knowl- 

 edge, must have contained hard parts. From a depth of 860 fathoms 

 (Station No. 41) comes an immature Serpula tube with the worm 

 (Ditrupa 1) ; and as from the same locality fragments of mud tubes are 

 found, it is probable that the bottom is muddy, though perhaps not 

 exclusively so.* The relations of temperature are not yet known to 

 me from either locality. 



* It is not uncommon in the deep water of the Gulf of Mexico to bring up rocky frag- 

 ments from great depths, which, judging from the amount of mud brought up by the trawl 

 at the same time, must have formed isolated patches. Of this I shall say more hereafter, 

 when speaking of the characteristic features of the bottom of the Gulf of Mexico. As far 

 as the temperature is concerned, I am preparing a general sketch of the temperature of 

 the waters of the Gulf of Mexico, which is to appear in one of the forthcoming numbers of 

 the Bulletin, illustrated by a selection from the numerous serial lines of temperatures taken 

 by Lieutenant-Commander C. D. Sigsbee during the past four years. I may merely state 

 here, in a general way, that, the surface varying from 74° to 80°, at a depth of 100 fathoms 

 the temperature varies from 58° to 71° ; at 200 fathoms, from 48° to 65° ; at 300 fathoms, 

 from 44° to 63°; at 400 fathoms, from 41° to 61° ; at 500 fathoms, from 40° to 56°; at 600 

 fathoms, from 39i° to 47°, while below 600 fathoms to 2000 fathoms, it varies from the 

 above to 39°; the sections from Tortugas to the Yucatan Bank showing a higlier tem- 

 perature than we find in the section from the mouth of the Mississippi to the Yucatan 

 Bank. A section of still higher temperatures is shown across the line running from 

 Cape San Antonio to the Yucatan Bank, a section of somewhat lower temperature 

 across from Tortugas to Port Mariel (Cuba), and cue very slightly lower still from Cape 

 Florida to Gun Key. — Alexander Agassiz. 



CAMBBmoE, May 1, 187y. 



