184 HYALOPATINA. 



The shell is of a primrose yellow color, thin, concentrically striated, 

 and with a few obscure radial ridges. The animal is of a deep port- 

 wine colour ; the foot is circular in outline, with an extended mar- 

 gin ; the under side of the mantle is covered with small white car- 

 unculse. 



Dimensions. Transverse diameters, 19 and 15 ; height, 4 mill. 

 (Tote). 



Lower end of the South Channel of Port Phillip, seven to sixteen 

 fathoms, sand and weed (J. B. Wilson); St. Vincent Gulf, S. Aus- 

 tralia. 



Umbrella corticalis TATE, Trans., Proc. and Rep. Roy. Soc. S. 

 Australia, xi, p. 65, pi. 11, f. 11 (April, 1889); Rep. Austr. Asso. 

 Adv. Sc., i, p. 336; and in WILSON, Proc. Roy. Soc. Viet, (new 

 series), ii, p. 66 (1890). 



Subgenus HYALOPATINA Dall, 1889. 

 Hyalopatina DALL, Bull. Mus. Comp. Zool., xviii, p. 61. 

 Shell dextral, flattened, sculptured, ovate, nucleus sinistral, im- 

 mersed. Soft parts unknown. 



H. RUSHII Dall. PL 51, fig. 58 (enlarged). 



Shell oval, translucent bluish-white, almost perfectly flat, ex- 

 tremely thin. Nucleus of less than one whorl, half immersed, the 

 remainder rising above the surface, smooth, not polished. Upper 

 surface nearly flat, except near the nucleus which is situated nearly 

 in the median line and close to the posterior margin ; concentrically 

 faintly undulated ; with faint concentric growth lines, and with very 

 numerous radiating lines of extremely minute slightly elevated 

 points, recalling the granules of Poromya on a much finer and more 

 minute scale. They are so small as to hardly appear elevated, but 

 more like radiating lines of opaque dots on the generally translucent 

 surface. Margin regularly ovate, entire, extremely thin. Under 

 surface of shell mostly polished, a little domed under the part in 

 front of the nucleus ; there are faint markings (interrupted on the 

 right side about the middle) which appear as if they might repre- 

 sent the area of muscular insertions, but the polish of the shell is 

 such that this is not definitely ascertained. The sides of the shell 

 are a little elevated, as if it had grown on a slightly con cave surface, 

 but the ends are depressed about to the same extent (Dall). 



Length 9'3, width 7*5; posterior margin to nucleus, 1'8 mill. 

 Of Great Isaac Light, Bahamas, in 30 fms. (Dr. W. H. Rush). 



