S.A. NAT., VOL. XIV. 
August 31st, 1933. By Bernard C. Coitoyi and F. K. Godjrey. 141. 
grows in de^th and width until it divides it into two. This groove 
may begin on the centre or on an}- part of the side of the rib. 
Idle ribs so formed may subsequently be cut up by other grooves. 
Sometimes two or three of such furrows may appear on the same 
rib at the same time and enlarging at an equal rate form three 
or four subequal riblets. The contour of the ribs may vary 
greatly, they may be narrow and comparatively high throughout 
their length, or they may almost fade out and leave the anterior 
part of the shell nearly smooth. The shape of the ribs may also 
change; they may have concave Interstices so as to resemble a 
fluted column, then the ribs may widen out and become convex, 
wh.ile their interstices become reduced to narrow, shallow grooves 
between broad, approximate, rounded ribs. Pilsbry suggests 
the typical form is hexagonal; usually there are more than six 
costae. I’he anal appendical tube usually wanting, even during 
life; when present it may be two or three millimetres long; it is 
central, but not always in the axis of the shell; it is probably an 
outgrowth subsequent to truncation, and not merely a residual 
inner laver of the shell after the outer portion has been absorbed. 
D. duodecimeostatum Brazier 1877. “The IVelve-ribbed 
Dentalium.” Straight, thin, shining, six-sided, white; longitudin- 
al ribs rounded, the base with twelve, and from the centre to 
the apex six, interstices smooth; apex tapering, entire, rvith minute 
perforation; aperture large, l.ength 22, diam. apex .5, base 2 
mm. Ciulf St. \incent, 22 fathoms. (Type locality — Darnley 
Island, 'rurres Straits. 30 fathoms, sandy mud). South Aus- 
tralian specimens do not exceed 18 mm. and are probably sub- 
speciiically distinct. 
D, cheverli Sharp & Pilsbry 1898 (= D. seplemcosiattim 
Brazier 1877, [rcocc.). “The Chevert Expedition Dentalium.’^ 
Slightly arched, white; ribs seven, somewhat sharp, having finer 
ones between, extending from base to centre, interstices with fine 
transverse silk-like striae; apex perforated, perforation with a 
minute noich-Iike fissure on dorsal margin; aperture circular, en- 
tire. Length 14, diam. apex .3, base l.S mm. Gulf St. Vincent, 
22 fathoms. (Type locality — Evan Bay, Cape York, North Aus- 
tralia. 6 fathoms, sand). 
D. katowense Brazier 1877. “The Katow Dentalium.” 
'J'liin. transparent, slightly arched near the apex; white; ribs 
seven throughout, fourteen from the centre to the base, thosi? 
above being most conspicuous; interstices with minute lengthen- 
ed striae; apex thickened, perforation small, entire; ayerture 
cnrcular. Length 14, diam. apex 1, base 2 mm. Gulf St. \'in- 
