MOLLUSCA FROM KKJIIT HUNDRED FATHOMS — HKDLEY. 363 



The posterior radial ribbing recalls C alcocki, Sinith^'' from the 

 Bay of Bengal, from which the abbreviated rostrum rearlily dis- 

 tinguished the Australian species. 



ThYASIRA ALHKJKXA, sp. IMV. 



(Plate Ixvi., fig. 4, .5). 



Shell minute, rather higher than long, translucent with faint 

 growth lines. Anterior margin slightly sinuate, ventral rather 

 .straight, postei'ior rounded. Fold almost obselete. Umbo pro- 

 minent, median, incurved. Muscle scars opaque, solid, projecting 

 above the interior surface and visible from the outside. Height, 

 2 ; length, 1-9 ; depth of single valve, 0-75 mm. 



A few separate valves. 



This species is very distinct from any yet recorded from 

 Australia. It appears to belong to the sub-genus Axiun/.us,'-^ 

 characterised by the absence of the fold, but is narrower with 

 more prominent umbo than any referred to that group. The 

 white cheeks of the opaque adductor scars contrasted with the 

 translucent shell are a convenient recognition mark for the 

 species. 



Lucina induta, sp. nor. 



(Plate Ixvi., fig. 11, 12). 



Shell minute, very thin, brittle, glossy, white, concealed beneath 

 a thick hard brown mass which cakes, cracks and splits oft' when 

 dry. In shaj^e subcordate, rounded anteriorly, subangled pos- 

 teriorly, beaks prominent incurved. Lunule absent. Sculpture, 

 irregular concentric undulations and striations. No muscle scars 

 visible. Hinge, tlie valve margin is produced under the umbo to 

 simulate a cardinal tooth, the ligament occupies a naiTow groove. 

 Length, 3 ; height, 265 mm. 



Several complete specimens, from 800 fathoms. 



As usual with thin sliells the muscle scars are invisible, indeed 

 so few salient characters are presented that the systematic position 

 of the species is uncertain. Possibly it may enter Vaticinaria.-^ 



'■' Siiiitli-Aiiii. Mug. Nut. Hist., (8), xiv., 1«9-1, j). 170, \^\. v., f. 8. 

 ■M V'^crrill and Busli— Proc. U. S. Nat. :\Ius , xx., 1898, p. 790. 

 '■" J)all— rroc. f. S. Nat. Mur., xxiii., 1901, p. 830. 



