I04 



•ENDEAVOUK" SCIENTIFIC RESULTS. 



RiSSOA VERCOXl.WA, Sp. )lOV. 



(Plate xix., fig. 23.) 



Shell small, ovate, thin, translucent. Colour white. Whorls 

 four, rounded and parted by deep sutures. Sculpture : First 

 whorl and a half smooth, next with about twenty-five sharp 

 though delicate radial ribs, these increase till on the last whorl 

 they amount to about forty, below the periphery they fade 

 gradually. Different individuals vary in the development and 

 number of these radials. On the last whorl eight or ten spirals 

 equal in grade to the radials override them, thus enclosing 

 rectangular meshes. On the upper whorls the spirals grad- 

 ually vanish, so that on the base are spirals alone and on the 

 upper whorls radials alone. A secondary microscopic sculp- 

 ture of close spiral scratches is most conspicuous in the meshes 

 of the body whorl. Aperture subcircular, angled above. 

 Outer lip fortified by a slight external varix, columella margin 

 expanded and reflected over a small umbilical furrow. Length 

 2, breadth i "25 mm. 



This species is closely related to R. filosa, Hedley and 

 Petterd,! from the east coast, but that is larger, has an extra 

 whorl and is more coarsely sculptured. That the difference 

 is not due to growth is shown by the contrast between the 

 upper whorls of the two species. The novelty is dedicated to 

 Dr. J. C. Verco, who has done such admirable work on the 

 Marine Mollusca of South Australia. 



Hah. — Numerous specimens from too fathoms forty miles 

 south of Cape Wiles, South Australia. 



Amphithalamus costaus, sp. no7'. 

 (Plate xix., fig. -'4.) 



Shell small, rather solid, imperforate, narrowly oblong, 

 glossv. Colour uniform ivory white. Whorls fi\e, including 

 a smooth turbinate protoconch of two whorls. Adult whorls 

 wound obliquely, parted by a deeply channeled suture. Sculp- 

 ture : Broad, flat radial ribs of irregular breadth, crowded on 

 the last half whorl, their ends denticulate the summits of the 

 whorls. So sharp and narrow are the interstices as to resemble 

 cracks. On the last whorl the radials amount to twenty-two. 

 Aperture trumpet-mouthed, oblique, submedian. Length 3, 

 breadth i'l,. 



Attempts ha\e been made by Tryon2 and b\- Tate^ to sub- 

 divide the RLssoa of Australia into groups. These arrange- 

 ments, though helpful, cannot be regarded as final. If only 



1 Hedley & Petterd— Rec. Austr. Mus., vi., 1906. p. 217, pi. xxxvii.. f. 2. 



2 Tryon— Man. Conch., ix., 1887, pp. 314-69. 



5 Tate— Trans. Roy. Soc. S. Austr., xxiii., 1899. pp. 232-7. 



