66 NEW SPECIES OF TASMANIAN MOLLUSCA, ETC. 



spectively umbilicate to the apex. Aperture roughly- 

 quadrangular, wider than the height of the shell ; at the 

 outer edge bidentated by the keels. 



Diameter, 1 ; height, about .4 mill. 



Type, with a few others, from Frederick Henry Bay, 

 taken from the roots O'f the giant kelp. 



Thisi minute shell has a consideraTole resemblance to 

 Cyclostrema bastowi, Gatliff, the type of Orbitefitella, and I 

 consider it congeneric; probably C. mayii, Tate, should 

 also be included in this genus. 



Note. — The specimen from which the drawings were 

 made was accidentally destroyed. 



PI. XVI., figs. 23, 23a, 23b. 



Patelloida corrodend.a., sp. nov. 



Shell roundly oval, rather depressed, apex one-third 

 from the anterior end, exterior fvirnished (in the type), 

 with 20 radiating, smooth ribs, irregularly spaced, which 

 extend from the summit to the margin, and several shorter 

 ones, intercalated near the margin. The ribs are but 

 slightly raised, dull white, the wider interspaces being- 

 black, apex eroded. Interior margin black, bearing white 

 triangular spots opposite the ribs, with their sliarper 

 points towards the edge. Behind these is a narrow 

 purplish ring, then bluish, with a brownish-white centre. 



Length, 14; breadth, 11; height, 5 mill. 



Type, from the western shore of Frederick Henry 



While fairl}?- constant in shape, it varies much in 

 the number of ribs, sometimes being nearly twice as 

 numerous as given above. The shell is often so much 

 corroded that the sculpture only remains on the marginal 

 third. The species is common at a spot near my home 

 living on large diabase boulders, at about half-tide. X 

 have not yet noticed it elsewhere ; it long escaped notice, 

 as it is associated with Siplwnaria diemenensi s of about 

 the same size and general appearance. As thev are ex- 

 posed to the air for several hours at every tide, they suffer 

 extremely from erosion, even quite small ones being badly 

 affected. It resembles P. flarnmea, Quoy and Gaim, in 

 general shape. ' That species is destitute of ribs, but has 

 fine axial striae, and a different interior coloration, and 

 lives near low water mark. 



PI. XVII., figs. 24, 24a. 



