MA RINK MOLLUSCA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 133 



Dentalium megathyris, Dall. 



Dentalium megathyris, Dall, Proc. U.S. Nat. Mus., xii. p. 293, pi. ix. fig. 1 (1889). 

 Stearns, Proc. U.S. Nat. Mus., xvi. p. 424 (1893). 



Hab. Lat. 71 22' S., 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, Macandrevia 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. majorinum, Roche b. 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 PROTOBKANCHIATA. 



Family Nucididse. 

 Yoldia profundorum, sp. n. (Plate, figs. 18, 18a, 18&). 



Y. testa parva, tumida, nitida, leevi, inaequilaterali, periostraco plumbeo-olivaceo contecta, antice^ 

 rotundata, postice paullulum producto, umbonibus erosis, approximatis, haud prominulis, ligamento obscure, 

 linear!, cardinibus utriusque valvae decem denticulis utrinque prseditis, pagina interna nitida, albo-lactea, 

 sinu palliali parvo. 



Alt. 3, Int. 4-50 mm. 



(ROY. BOC. EDIN. TKANS., VOL. XL VIII., 359.) 



