Rectobolivina sp. A

Hanagata, S & Nobuhara, T, 2015, Illustrated guide to Pliocene foraminifera from Miyakojima, Ryukyu Island Arc, with comments on biostratigraph, Palaeontologia Electronica (Cambridge, England) 33 (8), pp. 1-142 : 80

Rectobolivina sp. A

Figures 25.13, 25.14

1961? Siphogenerina aff. dimorpha (Parker and Jones) var. pacifica Cushman — LeRoy (Part 1), p. 37, pl. 3, figs. 97, 98.

Description. Test small and short for the genus, approximately 0.4 mm in length, 0.2 mm in breadth, 0.1 mm in thickness; triangular in front view, oval in transverse section; chambers not inflated, increasing slowly as added; surface wall coarsely pitted with pores; sutures slightly depressed, weakly limbate; aperture oval with marginal rim at the top of test.

Remarks. This species resembles Siphogenerina aff. dimorpha var. pacifica Cushman as illustrated by LeRoy (1961), in having a compressed test with coarsely pored wall. Siphogenerina dimorpha var. pacifica Cushman (1926) has a cylindrical test with a near-circular cross section.

Occurrence. Common in the lower part of the Yonahama Formation.

Figures

FIGURE 25. Family Stainforthiidae and Siphogenerinoididae. All scale bars = 0.1mm. 1, 2. Stainforthia tenuata (Cushman), 1: MPC-26510 from sample 8-2 (Yonahama Formation, PL4); 2: MPC-26511 from sample 15 (Yonahama F., PL3). 3, 4. Euloxostomum bradyi (Asano), 3: MPC-26239 from sample 8-2 (Yonahama F., PL4); 4: MPC-26240 from sample MK02B (Minebari F., PL5). 5, 6. Euloxostomum pseudobeyrichi (Cushman), 5: MPC-26241 from sample 5 (Minebari F., PL5); 6: MPC-26242 from sample 5-2 (Minebari F., PL5). 7, 8. Hopkinsinella glabra (Millett), 7: MPC- 26326 from sample 1 (Minebari F., PL5); 8: MPC-26327 from sample 14-2 (Yonahama F., PL4). 9, 10. Rectobolivina asanoi Murata, 9: MPC-26453 from sample 18 (Oura F.,?PL1); 10: MPC-26454 from sample MK02A (Minebari F., PL5); 9 microspheric form, 10 megalospheric form. 11, 12. Rectobolivina bifrons (Brady), 11: MPC-26455 from sample 17 (Yonahama F., PL2); 12: MPC-26456 from sample MK01 (Yonahama F., PL2); 11 microspheric form, 12 megalospheric form. 13, 14. Rectobolivina sp.A, 13: MPC-26457 from sample 6 (Yonahama F., PL2); 14: MPC-26458 from sample 17 (Yonahama F., PL2). 15. Sagrinella convallaria (Millett), MPC-26476 from sample 10 (Onogoshi F., PL2). 16, 17. Sagrinella durrandii (Millett), 16: MPC-26477 from sample 1 (Minebari F., PL5); 17: MPC-26478 from sample 5 (Minebari F., PL5). 18, 19. Sagrinella jugosa (Brady), 18: MPC-26479, 19: MPC-26480, both from sample MK01 (Yonahama F., PL2). 20, 21. Saidovina formosana (Nakamura), 20: MPC-26481, 21: MPC-26482, both from sample 18 (Oura F.,?PL1). 22, 23. Saidovina karreriana (Brady), 22: MPC-26483 from sample 5 (Minebari F., PL5); 23: MPC-26484 from sample MK02B (Minebari F., PL5). 24, 25. Rectuvigerina striata (Schwager), 24: MPC-26459 from sample 8-2 (Yonahama F., PL4); 25: MPC-26460 from sample 14 (Yonahama F., PL4). 26. Allassoida tonohamaensis (Takayanagi), MPC-26110 from sample 1-2 (Minebari F., PL5).