MARINE MOLLUSCA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 359 
Dentahium megathyris, Dall. 
Dentalium megathyris, Dall, Proc. US. Nat. Mus., xii. p. 293, pl. ix. fig. 1 (1889). 
5 Ps Stearns, Proc. U.S. Nat. Mus., xvi. p. 424 (1893). 
Hab.—Lat. 71° 22’ 8., long. 16° 34’ W., 1410 fathoms. Station 417. 
In our first report we allocated a large Dentalium dredged from 1410 fathoms to 
D. Shoplandi, Jouss., as it agreed with specimens so named in the British Museum 
¢ 
from “near Aden.” We have since received from the same station a large fragment 
of the upper part of a living specimen, evidently snapped off by the dredge, and a 
number of smaller fragments. Critical examination of these has led us to conclude 
that our specimens are identical with D. megathyris, Dall, which has occurred off 
Chiloe Island and south-east Chili in 1050 and 1342 fathoms, in the Gulf of Panama 
in 2282 fathoms, and other localities in the Panamic region. It is significant that in 
company with this Dentalium, both in the Gulf of Panama and in the 1410 fathoms 
locality, the Brachiopod, Macandreva diamantina, Dall, should also occur. The 
descriptions and figures of D. megathyris and D. Shoplandi, as given by TRyoN, are so 
widely different in every respect, both as to dimensions and sculpture, and other minor 
details, that although our specimens agree so well with the British Museum examples 
purporting to come from Aden, we now are inclined to refer them to D. megathyris, 
as, even if this species should ultimately be proved to be an extreme form of 
D. Shoplandi, that specific name would become a synonym—D. megathyris, Dall, 
having priority of five years. From a careful study of the material and literature at 
our command we cannot help thinking that D. megathyris, Dall, D. Shoplandi, Jouss., 
D. ceras, Watson, and perhaps D. majoriznum, Rocheb. and Mab., may. eventually 
prove to be but forms of one variable gigantic longitudinally costate Dentalium in 
the southern hemisphere, radiating towards the Atlantic as well as the Pacific Ocean, 
and inhabiting everywhere very deep water, where the great pressure, darkness, and 
equable temperature render it possible for it to range through many degrees of latitude. 
Class PELECYPODA. 
Order PROTOBRANCHIATA. 
Family Nuculide. 
Yoldia profundorum, sp. n. (Plate, figs. 18, 18a, 18). 
Y. testa parva, tumida, nitida, levi, inequilaterali, periostraco plumbeo-olivaceo contecta, anticé 
rotundata, posticé paullulum producto, umbonibus erosis, approximatis, haud prominulis, ligamento obscuro, 
lineari, cardinibus utriusque valve decem denticulis utrinque preditis, pagina interna nitida, albo-lactea, 
sinu palliali parvo. : 
Alt. 3, lat. 4:50 mm. 
