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- 
uncule. 
Dimensions.—Transyerse diameters, 19 and 15; height, 4 mill. 
( Tate). 
Lower end of the South Channel of Port Phillip, seven to sixteen 
fathoms, sand and weed (J. B. Wilson); S#. Vincent Gulf, S. Aus- 
tralia. 
Umbrella corticalis Tarr, Trans., Proc. and Rep. Roy. Soe. 8. 
Australia, xi, p. 65, pl. 11, f 11 (April, 1889); Rep. Austr. Asso. 
Adv. Sc., i, p. 386; and in Wrixson, Proc. Roy. Soc. Vict. (mew 
series), ii, p. 66 (1890). 
Subgenus Hyatopatina Dall, 1889. 
Hyalopatina Dau, Bull. Mus. Comp. Zool., xviii, p. 61. 
Shell dextral, flattened, sculptured, ovate, nucleus sinistral, im- 
mersed. Soft parts unknown. 
H. rusart Dall. PI. 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 concave 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. 
Off Great Isaac Light, Bahamas, in 30 fms. (Dr. W. H. Rush). 
