104 
S. baconi, Reeve. Of (2. 
S. baconi, Reeve, Conch. Icon., 1856, vol. ix., pl. vi., fig. 30; 
‘Pritchard & Gatliff, Proc. Roy. Soc. Vict., 1903, vol. xv. (n.s.), 
ypart 3, p. 221. 
Type loc.— “Swan River.” 
The three shells from the Cuming Museum in the Natural 
History Museum (Brit. Mus.), London, from Swan River, 
labelled S. baconi, Reeve, are similar to ours. It was given 
in Adcock’s Handlist, No. 455, as S. luzonica, Reeve; but the 
types of this species, and from which his figures were drawn, 
are from the Philippine Islands, and have only 9 to 13 ribs, 
much stouter than ours. S. baconi is probably the species 
catalogued by Tate & May in their Tasmanian Census as 
iS. albida, Angas, in Proc. Linn. Soc. New South Wales, 1901, 
‘vol. xxvi., p. 419. 
It has been taken’ from MacDonnell Bay to Streaky Bay, 
and up St. Vincent and Spencer Gulfs. It is found on the 
rocks in the South-Hast, which are completely exposed at low 
tide, and on the reefs which are not exposed; also on the 
ocean shore, subject to the rough seas from the break of the 
rollers, and the smooth water in the quiet bays and gulfs. 
The shells appear to be larger in the rougher South-Hast than 
‘in quiet places like Hallett Cove, etc. The size may reach 
30 mm. by 23 by 5°5. They are very flat, as low as 4°75 mm. in 
a shell of 25 mm., the greatest height being 6 mm. in a shell 
of 20 mm. They are mostly roundly elliptical, rarely nearly 
circular, more rarely oblong-elliptical. Usually they are quite 
thin, but those from rough water may be very solid. Gener- 
ally much eroded, especially when senile, they may show no 
sculpture. There may be only 17 to 20 ribs standing up 
validly above all secondary riblets, or there may be 44 nearly 
equal radii. Their colour is a dull white, rarely yellow. In 
‘some, especially in juveniles, or the earlier portions of mature 
ones, and in the thinner forms, tiny blackish or brownish spots 
‘may be scattered about irregularly, sparsely, or abundantly, 
or they may form clouds, rings, or patterns. The interior is 
quite white, the horseshoe amber-coloured. Sometimes within 
the horseshoe, and in a depression in front of it, and along 
the siphon furrow, is a fuscous clouding. The animal is of 
a light saffron-yellow colour. 
“S. albida, Angas. 
‘§. albida, Angas, Proc. Zool. Soc., Lond., 1878, p. 314, pl. ° 
-xviii., figs. 16, 17; Adcock, Handlist, etc., 1893, p. ii., No. 456. 
Type loc.—St. Vincent Gulf, South Australia. 
I examined the shell at the\Natural History Museum 
(Brit. Mus.), London, in 1899. It was mounted as “Type 
