208 
Type in Dr. Verco’s collection. 
I am inclined to think that even this species is but an 
extreme variant of the D. intercalatum, Gld. It would seem 
as though the more initial ribs are present at the posterior 
end, the fewer interstitial ribs arise, which is easily under- 
stood; and the more likely they are to be round and broad 
and encroach on the intercostal spaces. Still one may meet 
with an occasional specimen starting with 11, ribs which 
Increase up to 24, and are rather narrow; or with one which 
starts with only a few ribs, 7 or 9, and these become broad 
and rounded. re 
The following species of Dentalium appear to be distinct 
from Dentalium intercalatum, Gld., with its many varieties : — 
Dentalium hemileuron, n. sp. Pl. xxvi, fig. 2. 
Shell long and narrow, very slightly curved, mostly at: 
the hinder part, white opaque when dead, translucent whe: 
fresh, and glistening, rather thick. There are 10‘axial ribs, 
valid, narrow, about one-fourth the width of their inter- 
spaces, less valid and less distant on the convex side. Well 
developed in the posterior half, then becoming quickly obso- 
lete and absent from the anterior third. There is no increase 
in number as the shell grows larger, close transverse’ ‘scratch 
marks, and circles of varying opacity make the ornament. 
Anterior aperture round. Posterior aperture round, but on 
the convex surface it has a sinus about as deep as wide with 
convex margins. 
Dimensions,—Length, 30 mm. ; greatest width, 2°4 mm. ; 
smallest, “4 mm. 
Locality.—Dredged in 300 fathoms off Cape Jaffa, type 
with 20 in good condition (some alive), 51 in poor; in 130 
fathoms off Cape Jafia, 37 (some alive); in 150 fathomis off 
Beachport, 1 poor; in 200 fathoms, 1 moderate. 
In a young individual the ribs are traceable to within 2 
mm. of the end, where the diameter was only ‘3 mm., beyond 
which ribs were absent and only transverse scratchings. were 
visible; the extreme 2 mm. cap, as it were, the part beyond. 
The largest example measures 34 mm. Some have 9 ribs, 
some 8, some ll. 
Diagnosis.—There are no axial interstitial riblets. as in 
D. thetidis, Hedley, nor increase in the number. of ribs by 
splitting or intercalation, as in D. intercalatum, Gld., and 
the anterior part is ribless. ; 
Type in Dr. Verco’s collection. 
