438 DISCOVERY REPORTS 



409. Nonionella auris (d'Orbigny) (Plate XVI, figs. 17-19). 



Valvidina auris, d'Orbigny, 1839, FAM, p. 47, pi. ii, figs. 15-17. 



Nonionella amis, Cushman and Kellett, 1929, WCSA, p. 5, pi. i, fig. 9; pi. ii, figs. 2, 3. 



Seven stations: 228; WS 76, 83, 86, 210, 215, 225. 



Never frequent, indeed generally rare, but a good many specimens have been ob- 

 tained. Most numerous at WS 83, where it was found of all sizes. The best specimens 

 at WS 215, 225 ; at 228 and WS 210 all the specimens were very small. Large specimens 

 measured 0-50 mm. in breadth, 0-40 mm. in width and 0-30 mm. in thickness at the oral 

 face. 



D'Orbigny's species is a typical Pacific form. He does not record it at all from the 

 Falkland Islands, but only from the Chilean and Peruvian coasts "between 34° S and 

 the equator", and he records it as very common, in fact at Payta the species "formed 

 j(jihs of the material gathered". There are two Type tubes in Paris. One marked 

 "Chile and Peru" contained no specimens of A^. auris, but varieties of N. scapha and 

 A'^. boueana. The second tube labelled "Amerique meridionale" contains specimens 

 identical with those which we figure. 



410. Nonionella iridea, sp.n. (Plate XVI, figs. 14-16). 

 Six stations: 236; WS 93, 217, 221, 248, 433. 



Test minute, hyaline, consisting of about 12-14 chambers, arranged inaequilaterally 

 in an evolute spiral. Six or seven of the chambers are exposed on one side of the test, 

 the whole of the series more or less visible on the other. The primordial chamber often 

 appears as a central boss. Sutures depressed, and chambers more or less inflated. 

 Peripheral edge broad, slightly lobulate. Colour glassy to white, often iridescent owing 

 to diffraction spectra caused by the thinness of the shell. 



In appearance this little shell bears considerable resemblance to Nonionella aim's 

 (d'Orbigny), though difTering in the number of chambers and size. It was at first thought 

 that it might have some connection with the life-history of that species, but this theory 

 was abandoned when its distribution was found to be quite difl^erent. Zoologically, we 

 think that it is probably no more than a starved and pauperate form of A^. scapha 

 (Fichtel and Moll) which has assumed the inaequilateral {Nonionella) mode of growth 

 perhaps as a result of unfavourable conditions of existence. It is much more abundant in 

 the South Georgia area, where it is frequently one of the dominant species, than in the 

 Falklands ; its limited distribution in the latter area may perhaps indicate that it is an 

 introduced form which has not yet succeeded in establishing itself widely. 



There is a considerable amount of variation in the degree of inflation of the chambers, 

 and this, in its turn, affects the general appearance of the shell. 



Breadth averages 0-20 mm.; width, 0-15 mm.; thickness at oral face, o-ii mm. 



411. Nonionella chiliensis, Cushman and Kellett (Plate XVI, figs. 11-13). 

 Nonionella chiliensis, Cushman and Kellett, 1929, WCSA, p. 6, pi. ii, figs. 4 rt-r . 



One station: WS 91. 



