34 BULLETIN 161, UNITED STATES NATIONAL MUSEUM 



AMPHISTEGINA MADAGASCARIENSIS d'Orbigny 



Plate 11, Figure 3; Plate 12, Figures 1, 2 



Amphistegina madagascariensis d'Orbigny, 1826, Ann. Sci. Nat., vol. 7, p. 304. — 

 Fornasini, 1903, Rend. Accad. Sci. Istit. Bologna, vol. 7, p. 3, pi. 2, fig. 

 5.— Cushman, Todd, and Post, 1954, U.S. Geol. Surv. Prof. Paper 260-H, 

 p. 362, pi. 90, figs. 1, 2.— Todd, 1957, U.S. Geol. Surv. Prof. Paper 280-H, 

 p. 296, pi. 93, fig. 13.— Graham and Militante, 1959, Stanford Univ. Publ., 

 Geol. Sci., vol. 6, no. 2, p. 104, pi. 16, figs. 9-11. 



This species was described from Madagascar and probably has a 

 worldwide distribution in the equatorial belt. It is characteristic of 

 the littoral and shallow-water regions but exhibits a considerable 

 range of variation, dependent probably upon depth and turbulence of 

 water, with many transitional forms connecting the several variants. 



In the Albatross collections, the heavy-shelled, thick, usually orange 

 tests with blunt periphery and indistinguishable sutures (pi. 11, fig. 3) 

 are found most abundantly in the beach sands and in the near-shore 

 sediments. From farther out or deeper, the tests, though similar in 

 form, are smaller, white, and less abundant. Another variant (pi. 12, 

 figs. 1, 2), typical of lagoonal environments, trends toward a large, 

 white test with a more pinched-together periphery bordered by a 

 slightly limbate keel, and with the sutures fairly visible on both sides 

 of the test. 



The number of chambers per final whorl in Amphistegina mad- 

 agascariensis varies from about 9 to 15 or more. The supplementary 

 chambers on the ventral side are slender and curved backward at 

 their outer ends, which fail to reach to the periphery. Sutures on 

 both sides of the test are strongly curved but not characteristically 

 angled as they are m A. radiata. The raised umbilical areas on both 

 dorsal and ventral sides are transparent, permitting a view into the 

 interior of the test, sometimes a view of the proloculus. 



AMPHISTEGINA RADIATA (Fichtel and Moll) 



Plate 13, Figures 1-3; Plate 14, Figures 1-3 



Nautilus radiatus Fichtel and Moll, 1798, Testacea microscopica, p. 58, pi. 8, 

 figs. a-d. 



Amphistegina radiata (Fichtel and Moll). — Cushman, 1924, Carnegie Instit. 

 Washington, Publ. 342, p. 49, pi. 17, figs. 1, 2.— Said, 1949, Cushman 

 Lab. Foram. Res., Spec. Publ. 26, p. 38, pi. 4, fig. 10.— Cushman, Todd, 

 and Post, 1954, U.S. Geol. Surv. Prof. Paper 260-H, p. 362, pi. 90, fig. 3. 



This is the deep-water species of Amphistegina, originally described 

 from the Red Sea. It is nowhere found abundantly in the present 



