66 NEW SPECIES OF TASMANIAN MOLLUSC.A, 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 of the giant kelp. 



This minute shell has a considerable resemblance to 

 Cychjutretiia hasfow/, Gatliff, the type of Orhite>ifel!a, 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 corrodenda, sp. nov. 



Shell roundly cval, rather depressed, apex one-third 

 from the anterior end, exterior furnished (in tlie 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 sharper 

 ])oinfc3 towards the edge. Behind these is a narrow 

 pui'plish ring, then bluish, with a brownish-white centre. 



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



Type, from the western shore of Frederick Henry 



While fairly 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. 1 

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

 as it is asisociated with Siphonarin (liemenenais 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. fhimmea, Quoy and Gaim, in 

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

 fine axial strias, and a different interior coloration, and 

 lives near low water mark. 



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



