207 



Dentalium decemcostatum, Brazier. 

 Dentalium decemcostatum, Brazier, Proc. Linn Soc., N.S.W., 

 1877 vol. h\, p. 55. Type locality — Katow, New Guinea, 8 

 fathom*, sandy mud (Chevert Exped.); Pilsbry and Sharp, 

 Tryon, Man. Conch., 1897-8, vol. xvii., p. 8; Bossevain, Scapho- 

 poda, Siboga Exped., 1906, p. 27. 



Dredged in 15 to 22 fathoms in Gulf St. Vincent, 10 

 good; with 10 ribs throughout, with 10 ribs posteriorly, and 

 more than 10 anteriorly, 24 good. 



Dentalium francisense, n. sp. PI. xxvi., figs. 1 and la. 



Shell moderately solid, narrow, curved, less anteriorly r 

 translucent white, with 14 broad, low, round ribs extending 

 throughout, separated by distinct linear interspaces. Fine 

 transverse microscopic growth lines. Anterior aperture cir- 

 cular, margins thin, scarcely scalloped. Posterior end trun- 

 cate, aperture small, border thick, shape oval, elongate 

 an tero- posteriorly . 



Dimensions. — Length, 28 mm. ; diameter — anteriorly,. 

 3' 2 mm. ; posteriorly, 1'6 mm. A much younger individual 

 measures 13*5 mm. in length, 2'4 mm. in its anterior 

 diameter, and 8 mm. in its posterior. It is much more curved 

 and has a slightly projecting appendical tube. 



Locality. — In 15 to 20 fathoms in Petrel Bay, St. Fran- 

 cis Island, type with 4 others (2 alive) : in 35 fathoms off 

 St. Francis Island, 1 good ; in 15 to 22 fathoms in Gulf St. 

 Vincent, 9 good ; in 55 fathoms north-west of Cape Borda, 

 1 good; in 15 fathoms in Geographe Bay, Western Australia, 



I good. 



This shell varies. There may be only 11 ribs through- 

 out, of which I have two examples from Gulf St. Vincent, or 



II ribs posteriorly, and more anteriorly up to 22 from inter- 

 calated riblets, 13 examples from the same locality. 



T'here may be 12 ribs posteriorly and 12 anteriorly, and 1 

 these may be typically broad and round, or rather narrow 

 and flat, 4 examples ; or of intermediate width, 9 examples ; 

 or 12 ribs posteriorly and 2 or more additional riblets 

 anteriorly, 4 examples, all dredged in 15 to 22 fathoms in 

 Gulf St. Vincent. 



There may be 13 ribs throughout, as in 11 examples from 

 15 to 22 fathoms in Gulf St. Vincent. 



There may be 15 ribs throughout, as in 9 examples from 

 15 to 22 fathoms in Gulf St. Vincent. 



There may be 18 ribs throughout, as in 1 example from 

 Port Lincoln, but this is a large old individual, with a rela- 

 tively great posterior diameter, and probably had fewer ribs 

 earlier in life. 



