14 THE VOYAGE OE H.M.S. CHALLENGER. 



rounded. Sculpture: The angles of the shell project more or less in a sharp rounded 

 rib, which is sometimes double; there are a few longitudinal striae, regular, O'Ol in. 

 apart, strongest near the angles, more or less obsolete as they recede from these. Neither 

 end is fresh enough for description. L. 0'47 in. B. 0"049. 



I have hesitatated a good deal in separating this from Siphodcntalium tctragonum, Broc. = 

 quinquangulare, E. For., with which it agrees more closely than with Siphodcntalium pentagonum, 

 Sars. Here, however, the longitudinal ribs are much closer, as well as much more obsolete ; the 

 shell is more curved throughout its whole length, is more attenuated, and retains its square form 

 and sharp angles instead of becoming rounded as in Siphodcntalium tctragonum, Brocchi. Amidst 

 all the variations of that very variable form I have not seen any that connects it with this species. 



2. Siphodentalium tytthum, 1 Watson (PI. II. fig. 5). 



Siphodentalium tytthum, Watson, Prelim. Report, pt. 2, Journ. Linn. Soc. Lond., vol. xiv. p. 520. 



Station 24. March 25, 1873. Lat. 18° 38' 30" N., long. 65° 5' 30" W. N. of 

 Culebra Island, West Indies. 390 fathoms. Pteropod ooze. 



Shell. — Minute, very conical, i.e., broadening rapidly, much bent, very thin, but not 

 hyaline, apparently horny when living, and becoming opacpie when dead, and then also 

 glossy but not brilliant. Sculpture : Some very faint traces of circular strias on the lines 

 of growth. Mouth-edge very thin and chipped. Apex broken, but in one specimen 

 showing the two lateral clefts common in the genus. L. - 22 in. B. at mouth 0'049 ; at 

 apex 0-013. 



In texture and in general form this is like Siphodentalium vitreum, Sars, but it broadens much 

 faster and is more curved. 



3. Siphodentalium pusillum, Watson (PI. II. fig. 6). 



Siphodentalium pusillum, Watson, Prelim. Report, pt. 2, Journ. Linn. Soc. Lond., vol. xiv. p. 520. 



Station 85. July 19, 1873. Lat, 28° 42' N., long. 18° 6' W. Palma, Canaries. 

 1125 fathoms. Volcanic mud. 



Shell. — Minute, attenuated, slightly bent, thin, transparent, irregularly banded with 

 opaque white, which runs elliptically round the shell. Sculpture : There is no trace 

 of longitudinal striae, but the whole surface is sharply scratched with minute transverse 

 striae, which run (as usual) not directly round the shell, but advance on the concave and 

 retreat on the convex curve. L. 0'12 in. B. at small end 0'01 ; at broad end 0'02. 



1 rurSog, smalL 



