274 BULLETIN OF THE MUSEUM OF COMPARATIVE ZOOLOGY. 
they are, like the Opheliidz, less characteristic of the localities to 
which they belong than the Maldanide and especially the Amphareti- 
die, whose large tubes, built of mud, and sometimes associated with 
those of the Eunicidz, 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 Serpulide 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 Serpulide 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?) ; 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. 
* Tt 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 394° 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 higher 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 one very slightly lower still from Cape 
Florida to Gun Key. — ALEXANDER AGASSIZ. 
CAMBRIDGE, May 1, 1879. 
