MELVILL AND STANPEN : MARINE SHELLS FROM LIVELY ISLAND. I05 



white, scarcely shining, the palHal Hne to some extent sinuous, but 

 not very distinct. 



Chione (Omphaloclathrum) exalbida Chemn. — Three ex- 

 amples, varying in growth and development. A massive, flat, oblong 

 shell, with raised concentric striae. Occurs in Straits of Magellan. 



Cryptodon falklandica E. Sm. — A shell with some affinity to 

 Axtnus Jlexuosus Mont. 



Saxicava antarctica Phil.— A stout coarse shell, found burrow- 

 ing in the roots of the large seaweed. Recorded from coasts of 

 Chili (Paetel). 



Thracia antarctica sp. n. (PI. I., figs. 13, 13a). 



T. testa defonni, fere ceguivalvi, sordide alba, tefiui; valvis ambabus 

 concenirice riidistriatis, convexis, titrimqiie hiulcis, anticc rotundatis, 

 postice tmncatis, bntntieo-sordescentibus, rudilamellosis; umbonibus in 

 uno specimiiie promitiulis, incunns, co?itiguis, in altera fere immersis ; 

 margine dorsali postice paullum excavato, antice leniter declivi, veutrali 

 fere recto; dente caidinali magtw, cochleari ; S2{perficie interna alba, 

 paiilliini prisinatica, linea palliali obscura, siniiosa. Lat. 15, alt. 11, 

 diani. 6 mm. 



To some extent resembling T. distorta Phil, from North Europe, 

 or T. cuneolus Rv., this very interesting little form differs from both 

 in decidedly less rotundity of outline ; it is, indeed, a far more typical 

 eu-Thracia, though to some extent liable to the SaxicavaASVo. deformity 

 so often present in our North European Th. distorta. 



It is of a dirty white, posteriorly stained with brown, and truncate, 

 anteriorly rounded, the umbones contiguous and prominent in one 

 specimen, while in another they are almost immersed ; the dorsal 

 margin is posteriorly slightly excavate, anteriorly gently sloping, the 

 ventral margin almost straight. The surface is concentrically rudely 

 striated, the valves convex, almost equal. Interior surface slightly 

 nacreous, whitish, pallial line obscure, sinuous. 



Only one Thracia (T. similis Conr.), of quite a distinct group, has, 

 till now, been reported from South American shores. 



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