Boone, Molltcsca, Cruises of "Ara" and "Alva" 315 



Family: PTERIIDAE 



Genus: PTERIA Scopoli 



Subgenus: Electroma Stoliczka 



Pteria (Electroma) electrina Reeve 



■f 



Plates 125 and 126 



Type: Reeve's type was collected in the Moluccas and origi- 

 nally deposited in the Cuming Museum. The greater portion of 

 the Cuming collection is in the British Museum of Natural His- 

 tory. 



Distribution: Moluccas (Reeve) ; Samoa (Boone). 



Material examined : One small specimen, collected in Pago- 

 Pago, Samoa, September 2, 1931. 



Technical description : The shell is rich reddish amber, with 

 the external surface marked by rays of lighter yellow-amber and 

 slightly concentric tones of blackish green on the umbo. The inte- 

 rior has the proximal suboval area beneath the organism paved 

 with an exquisite satiny white opalescent pearl, beyond which the 

 orange-amber surface of the outer portion is glistening. 



Shell obliquely oblong-subovate or subtrapezoidal, inequivalve, 

 the right valve being less convex, flattish, the left valve moder- 

 ately convex, with the greatest inflation from the umbo obliquely 

 toward the posterior margin ; the right valve less convex, flattish ; 

 the hinge margin is short, the greater portion of the dorsal margin 

 obliquely receding to the posterior ; the umbo is not very promi- 

 nent in the present young specimen, but is figured as moderately 

 so in larger shells by Reeve ; the anterior auricle is small, beaklike. 

 Faint concentric growth lines are present. The white dots de- 

 scribed by Reeve as a part of the external colour pattern appear to 

 be extraneous calcareous deposits when examined microscopically. 

 The exquisite colouration of this species, enhanced by its translu- 

 cency and extreme fragility and its distinctive oblong-subovate 

 shape, readily distinguish it from other members of the genus. 



The present specimen has a long diameter of 35 mm. Reeve 

 has figured specimens vdth a long diameter of about 50 and 70 mm. 



References: Avicula electrina, Reeve, Lovell, Conch. Icon., 

 1858, vol. X, Avicula, pi. 12, fig. 43-a-b, text opposite (March, 

 1857). 



