TROPICAL PACIFIC FORAMINIFERA OF "ALBATROSS" 33 



Genus SPHAERIDIA Heron-Allen and Earland, 1928 



SPHAERIDIA PAPILLATA Heron- Allen and Earland 



Sphaeridia papillata Heron-Allen and Earland, 1928, Journ. Roy. Micr. Soc, 

 vol. 48, p. 294, pi. 2, figs. 27-33; pi. 3, figs. 34-37. 



A single specimen, about 0.5 mm. in diameter, was found in the 

 sample from 40-50 fathoms off Fiji. 



Family AMPHISTEGINIDAE 



Genus AMPHISTEGINA d'Orbigny, 1826 



AMPHISTEGINA LESSONII d'Orbigny 



Plate 11, Figure 4 



Amphistegina lessonii d'Orbigny, 1826, Ann. Sci. Nat., vol. 7, p. 304, pi. 17, 

 figs. 1-4; Modeles No. 98, IV e livr. — Phleger and Parker, 1951, Geol. 

 Soc. Amer. Mem. 46, pt. 2, p. 26, pi. 13, figs. 13, 14; pi. 14, fig. 1. 



This large and beautiful species, originally described from Mauritius, 

 was not found in the Albatross collections from the southeastern 

 Pacific. It is included here only for comparison with the other two 

 species of Amphistegina that make up a rather conspicuous part of 

 the assemblages from the present collections. 



Judging from recorded occurrences, Amphistegina lessonii seems 

 to be much less abundant than either A. madagascariensis or A. 

 radiata. The only Pacific occurrence of A. lessonii that I know of is 

 at Kapingamarangi in the western Pacific, northeast of New Guinea, 

 where it dominates one of the facies. Study of the sedimentary 

 belts within this small atoll (McKee, Chronic, and Leopold, 1959) 

 revealed the restricted occurrence of Amphistegina lessonii between 

 approximately 120 and 210 feet in the central part of the lagoon 

 (idem, p. 526-527). 



At lesser depths within the same atoll a different species of Amphis- 

 tegina is found. Amphistegina madagascariensis, together with 

 Marginopora vertebralis, dominates the shallowest sedimentary belt 

 just inside the reef, being found mostly no deeper than 25 feet. 



These two species, living in mutually exclusive ecologic provinces 

 within an area of about 6 by 8 miles, are clearly distinct without any 

 transitional forms connecting them. A. lessonii is white and flat with 

 numerous (25-30) chambers that are clearly visible on the surface. 

 A. madagascariensis is orange, thick (with thickness equal nearly 

 to diameter), and the sutures so indistinct that the number of chambers 

 cannot be determined from the surface. In A. madagascariensis the 

 biconvexity is unequal, the dorsal side slightly less raised than the 

 ventral. 



