136 PROCEEDINGS OF THE NATIONAL MUSEUM vol.77 



SIGMOMORPHINA TRILOCULARIS (Bagg) 



Plate 36, figures 5 a-c 



Polymorphina trilocularis Bagg, U. S. Geol. Survej^ Bull. 513, 1912, p. 75, 



pi. 20, figs. 15-18. 

 Sigmomorpha trilocularis Cushman and Ozawa, Jap. Journ. Geol. Geogr., 



vol. 6, 1928, p. 74, pi. 16, fig. 5. 



Test small, ovate, more or less rounded at the base, rather acute 

 toward the apertural end; chambers much elongated and slender, 

 roundly triangular in cross section, slightly embracing, arranged in a 

 contraclockwise sigmoid series, each succeeding chamber removed 

 from the base; sutures depressed, distinct; wall smooth, thin; aper- 

 ture radiate. 



Maximum length 0.90 mm.; breadth 0.35 mm.; thickness 0.20 mm. 



Its elongated, slender chambers arranged in a more or less sigmoid 

 series are the characteristics of the species. Its sigmoid arrangement 

 of chambers is somewhat variable, and often it is closed, showing 

 more or less a quinqueioculine series. 



Distribution. — Only known in the North Pacific region as a late 

 Tertiary fossil and as a Recent species. We have the species from 

 the following localities : 



Recent. — Off coast of southern California. 



Pliocene. — Timms Point, San Pedro, Calif. Upper Pliocene, 

 Natsukawa, Province of Echigo, Japan. 



SIGMOMORPHINA YOKOYAMAI Cushman and Ozawa 



Plate 36, figures Q a, b 



Sigmomorpha (Sigmomorphina) yokoyamai Cushman and Ozawa, Contr. 

 Cushman Lab. Foram. Res., vol. 4, 1928, p. 18, pi. 1, fig. 16; Jap. Journ. 

 Geol. Geogr., vol. 6, 1929, p. 75, pi. 13, figs. 12-14; pi. 16, figs. 7, 8. 



Test ovate, greatest breadth toward the base, tapering toward the 

 apertural end, periphery sharply angled and carinate in the adult; 

 chambers comparatively few in the megalospheric form, more 

 numerous in the microspheric ; chambers elongated and very narrow, 

 arranged in an open sigmoid series and added so that the axis of each 

 chamber is somewhat oblique giving a peculiar twisted appearance 

 to the test; sutures distinct, very slightly depressed; wall thin, 

 transparent, with longitudinal costae which are continuations from 

 the ridges of the radiate apertures of each chamber, in some specimens 

 with additional costae covering the entire surface; aperture radiate, 

 terminal, somewhat produced into a cylindrical neck. 



Length of holotype 0.93 mm.; breadth 0.50 mm. 



This species is common and shows some variations in the surface 

 ornamentation, some of the specimens being smooth except for the 

 costae of the central portion, others being costate throughout. This 

 is one of the most striking species of the Japanese collection and is 



