308 THE VOYAGE OF H.M.S. CHALLENGER. 



This very fiue species has also been recorded from Yedo, Nagasaki, and Hakodadi, and 

 probably does not extend to California as stated by Reeve. 



Amussium, Klein. 

 Aimissiu7n plenronectes (Linne). 



Ostrca pleuronedes, Linii6, Syst. Nat., ed. 12, p. 1145. 



Pcden pleKronectcs, SowerViy, Thes. Concli., vol. i. p. 55, pi. xvi. figs. 127, 128, 135, 136. 



Peden pleiironedes, Reeve, Conch. Icon., vol. viii. pi. xiii. fig. 48. 



Habitat. — Station 203, Philippine Islands, in 20 fathoms ; and Station 188, south of 

 New Guinea, in 28 fathoms. 



The Philippine specimens of this well-known species are like that figured in Reeve's 

 work, but those from the North Australian region have the coloured valve curiously 

 ornamented with angular In-own markings, disposed somewhat regularly in radiating 

 series, and towards tlie umboncs the minute white dots which are usually noticeable are 

 arranged in rays also. 



Amussium dalli, n. sp. (PI. XXII. figs. 7-7c). 



Testa tenuissima, compressa, hyalino-albida, sequivalvis, elongata. Valvar sculptura 

 diversa ornatse, altera (? dextra) conspicue nitente, incrementi lineis striisque tenuissimis 

 sculpta, altera liris concentricis tenuibus ornata, undique minutissime cellulosa. Auriculae 

 parvse, subsequales, utrinque acute angulataj, in valva dextra lateribus paulo concavis. 

 Pagina interna fulgens, liris undenis radiantibus albis hand nd marginem productis instructa. 



This species is longer from the beaks to the lower margin than from side to side. It 

 is almost equivalve, the smoother valve, which I regard as the right, being perhaps a 

 trifle more swollen than the other. It is a very thin fragile shell, semitransparent and 

 very glossy, particularly the right valve, which has a more glossy appearance than the 

 left, the latter lieing of a somewhat thicker texture and of a dilute milky white colour. 

 The valves are differently sculptured. The right merely exhibits the fiue concentric 

 lines of growth and very fine radiating substrise. The left is more beautifully ornamented, 

 being concentrically closely and finely Urate, and throughout microscopically shagreened, 

 the outer or surface-layer being composed of countless excessively minute closely packed 

 crystal-like bodies having unequal sides, varying in number from four to six, and flat 

 outer and basal sui'faces. The beaks are acute, and converge to an angle of about 

 110 degrees. The ears are small, about equal on both sides, slighty concave laterally 

 in the right valve. The interior is very glossy, strengthened liy eleven fine 

 radiating co.stellse, which, with the exception of the two very short uppermost, only 

 extend about half-way across the surface of the right valve, and rather further in the 

 left, in which also they are a trifle thicker. 



