208 



Type in Dr. Verco's collection. 



I am inclined to think that even this species is but an 

 extreme variant of the D. intercalation, 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.^hich 

 starts with only a few ribs, 7 or 9, and these become broad 

 and rounded. 



The following species of Dentalium appear to be distinct 

 from Dentalium inter calatum, Gld., with its many varieties : — 



Dentalium hemileuron, n. sp. PL xxvi , rig. 2.- 



Shell long and narrow, very slightly curved, mostly 'at 

 the hinder part, white opaque when dead, translucent when 

 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': 1 ' '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 Jaffa, 37 (some alive) ; in 150 fathoms 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 11. .. 



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. inter calatum, Gld., and 

 the anterior part is ribless. .:' 



Type in Dr. Verco's collection. * 



