376 l>ll, H. L. JAMESON ON iSE [-^P^'- 1^' 



extreme. Posterior angle, formed bj the meeting of the hinge and 

 posterior margin of nacre, slightly obtuse, intermediate between 

 that of M. m. typica and \a,\\persim. Colour slightly darker than 

 in var. persica. White radii very distinct. Inside of lip oli^e- 

 greeu or brown. Nacre as in yax. persica but less silvery. Size 

 as in typica. 



Hah. Eed Sea. A specimen in the Museum from Aden, pre- 

 sented by Major Yerbury. 



[Moth er-of -Pearl dealers recognize three classes of Egyptian 

 shells, differing slightly in colour and lustre, viz., Jiddah (darkest), 

 Massowah (medium), and Aden (lightest). The last most closely 

 resembles var. persica.'] 



Var. e. M. margaritifera cumingi. 



Avicula camingii, Reeve, 1857, sp. 6 (Lord Hood 

 Island). 

 Type B.M. 



The Black-edged shell of Eastern Polynesia, known in the 

 trade as ' Tahiti," " Grambier," " Auckland," &c. shell. 



Eorm as in M. in. typica, but attaining greater dimensions ; at 

 times as much as 24-30 cm. in diameter, and often weighing six to 

 eight pounds per pair of valves. 



Colour deep glossy black, with, at most, very obscure traces of 

 the radial rows of spots. The latter are often quite suppressed. 

 Nacre steely in lustre, with a very broad margin of dark metallic 

 green, this border being wider and darker than in M. m. typica. 

 The " Tahiti," " Gambier," and "Auckland" shells of the trade 

 are distinguished by slight differences in form, but in colour they 

 all conform to M. cumingii of Reeve. 



Geographical Distribution. Tahiti ; Gambier Arch. ; Lord Hood 

 Isl. ; Penrhyn Group, and Eastern Polynesia generally. I am not 

 aware where the " Auckland " shells of the London markets are 

 tished. Their name is probably due to their being shipped j->er 

 Auckland from some Polynesian locality. 



Var. f. M. margaritifera mazatlanica. 



Margaritipliora mazatlanica, Hanley, 1855, p. 388, 



pi. 24. fig. 40 (Mazatlau, California). 

 Avicula barbata, Reeve, 1857, sp. 9 (Panama). Type 

 B.M. 

 " Panama shell " of the trade. 



This shell at first sight suggests a dwarfed and very convex 

 example of M. maxima rather than a geographical race of M. mar- 

 garitifera. It seems, however, to intergrade with the latter. 



The distinctive characters of this variety are its great convexity 

 and its aberrant shape and colour. 



The posterior angle is acute, or, more rarely, a right angle ; and 

 the posterior margin of the nacre slopes forward from the hinge, 

 much as in M. maxima, so that a perpendicular to the hinge, at 

 its posterior end, would fall entirely posterior to the border of 



