500 MOLLUSCA OF MAST HEAD RKEF, QUEENSLAND, II., 



and Pilsbry's comparison of BittiiLm scalatum Dunker,* suojgest 

 the inclusion of these Japanese species in Plesiotrochus. Nevill 

 has recorded the genus from the Indian Ocean. f Dr. J. C. Verco 

 has kindly sent me the radula and operculum of C. monacTius. 

 The former (PI. xvii., fig. 18) has the rachidian plate broad, with 

 a slender median cusp, not reaching the basal margin, with three 

 minute cusps aside. Laterals three, curved and hooked, the 

 hook of the innermost denticulate. Opercuknn (PL xvii., fig. 17) 

 thin, ovate, paucispiral. 



Mathilda oppia, n.sp. 

 (Plate xvi., fig.9.) 



Shell small, solid, ovate, narrowl}^ perforate. Colour ochreous. 

 Whorls four, plus a two-whorled tilted but not immersed proto- 

 conch. Suture deeply channelled. Sculpture : on the base are 

 three spiral threads, on the peripher}^ two prominent distant 

 spiral keels ascend from the aperture to the protoconch. These 

 are traversed by strong, widely spaced, perpendicular, radial ribs, 

 about seventeen to a whorl, which commence on the second adult 

 whorl and cease a little behind the aperture; they descend from 

 the suture to below the periphery and at the intersection of the 

 spirals form deep square pits. Aperture broadly ovate, outer lip 

 denticulated by the ends of the spirals, inner lip narrowly 

 reflected. Height 3-35 mm.; breadth 1-45 mm. 



A few specimens from 17-20 fathoms. 



Related to J/, decorata (Hedley, Mem. Austr. Mus. iv. 1903^ 

 p. 352, tig. 75) but differing by fewer spirals, smaller size and 

 different angle of the heterostrophe protoconch. 



TURRITELLA CAPTIVA, n.Sp. 



(Plate xvii., fig.26.) 



Shell of medium size, slender, slowly tapering to a fine point, 

 angled at the periphery. Whorls fifteen. Colour dull white 



* Pilsbry, Cat. Mar. Moll. Jap. 1895, p. 57. 

 t Nevill, List Mollusca Indian Museum, 1884, p. 158. 



