104 



S. baconi, lleeve. 



.S'. haroni, Reeve, Conch. Icon.. 1856, vol. ix., pi. vi.. fig. 30; 

 Pritchard & Gatliff, Proc. Rov. Soc. Vict., 1903,' vol. xv. (n.s.), 

 part 3, p. 221. 



Ti/pe loc. — "Swan River." 



The three shells from the Cuming Museum in the Natural 

 History Museum (Brit. Mus.), London, from Swan River, 

 labelled S. haconi, Reeve, are similar to ours. It was given 

 in Adcock's Handlist, No. 455, as S. luzoJiica, 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 

 S. 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 Soi^th-East, 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-East 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. 



S. albifla, Angas, Proc. Zool. Soc, Lond., 1878. p. 314, pi. 

 -xviii., figs. 16, 17; Adcock, Handlist, etc., 1893, p. ii.. No. 4o6. 



Tj/pe loc. — St. Vincent Gulf, South Australia. 

 I examined the shell at the Natural History Museum 

 i,(Brit. Mus.), London, in 1899. It was mounted as 'Type 



