CHAP. Il. ] TENERIFFE TO SOMBRERO. 189 
gulf-weed ; with many crustaceans, several of the nudibranchi- 
ate mollusca characteristic of the gulf-weed fauna, such as Scé/- 
lea pelagica and Glaucus Atlanticus, and many planarians. 
On the following morning the dredge was put over at 8 A.M., 
and line veered to 3000 fathoms; and at 10 o’clock we sounded 
in 2435 fathoms, sending down the slip water-bottle and a ther- 
mometer. The thermometer registered 1°-7 C., and the sample 
of the bottom in the “ Hydra” tube was still redder and more 
unpromising than in the sounding of the day before. 
The dredge came up at 4.15 p.m. with a small quantity of red 
mud, in which we detected only one single, but perfectly fresh, 
valve of a small lamellibranchiate mollusk (Fig. 45). In the 
Fig. 45.—Avicula (sp.). Greatly enlarged. (No. 16.) | 
mud there were also some sharks’ teeth of at least two genera, 
and a number of very peculiar black oval bodies about an inch 
long, with the surface irregularly reticulated, and within the 
reticulations closely and symmetrically granulated; the whole 
appearance singularly like that of the phosphatic concretions 
which are so abundant in the greensand and trias. My first 
impression was that both the teeth and the concretions were 
drifted fossils ; but on handing over a portion of one of the lat- 
ter to Mr. Buchanan for examination, he found that it consisted 
of almost pure peroxide of manganese. 
The character both of the exterior and interior of the nodule 
strongly recalled the black base of the coral which we dredged 
in 1530 fathoms on the 18th of February; and on going into 
the matter, Mr. Buchanan found not only that the base of the 
coral retaining its external organic form had the composition 
I.—13 
