522 



EEV. R. BOOG WATSON ON THE 



Sculpture. Most faint and delicate microscopic scratches on 

 the lines of growth, with a minute transverse flocculence and 

 some vague indication of longitudinal texture in the substance 

 of the shell. The mouth is large, very oblique, with a smoothly 

 rounded edge, which is sharp on the inner margin ; both it and 

 the posterior opening are oval. The ajpecc^ which is small, is 

 split on either side by a deep, narrow, slightly widening, smooth, 

 clean-cut, but not perfectly regular cleft, which is evidently 

 carried up the shell as the growth of the animal demands, for it 

 cuts across the transverse strise, as Mr. Searles Wood remarks is 

 the case with >S'. (DiscMdes) lijissum. Within the opening a 

 short, minute, longitudinal, rib-like process projects along the 

 middle of the posterior (i. e. convex curve) wall ; a little further 

 in a thin, narrow, circular callus runs round the opening. 

 L. 0-35. B. at mouth 0-032, broadest 0*055, apex 0-022. 

 This is much larger than S. tetrascMstum, W., and much less 

 cylindrical, being much more contracted towards the mouth. 

 The posterior internal rib is a curious feature. It shows through 

 the shell like a crack or depression, but is a true internal rib. 



6. SiPHODENTALITJM PRIONOTUM, W. {irpioviaTOS, jagged.) 



St. 185. Aug. 31, 1874. Lat. 11° 35' S., long. 143° 3' E. 

 Eaine Island, C. York. 155 fms. Sand. 2 specimens and 2 

 fragments. 



Shell. — Long, narrow, tapering, gently contracted at the mouth, 

 slightly bent throughout ; rather strong, polished, but hardly 

 brilliant, translucent white. Sculpture. Very faintly trans- 

 versely striated on the surface, and a very minute flocculence 

 in the same direction in the texture. Tor the breadth of 

 the shell the mouth is large, perfectly round, oblique, with a 

 smoothly rounded edge, which is sharp on its inner margin. 

 The apex is small, much chipped, but that in such a way as 

 in all the specimens to produce a shallow rounded hollow on 

 either side, with a sharp projecting point before and behind. 

 Within the opening a short excessively minute riblet runs out 

 along the middle of the posterior wall ; it shines through the 

 shell like a depression, being a little more transparent than 

 the shell-wall. L. 0-328. B. at mouth 0-028, greatest 0-039, 

 . at apex 0-013. 



This species diftera from the previous in being much narrower 



