502 MR. F. CHAPMAN ON SHERBORNINA: A NEW GENUS 



layer formed of small overlapping spatulate chamberlets. The primordial 

 series of about 7 globular to reniform segments, lying in the median system, 

 is discorbine — that is, depressed rotaline. Shell-wall perforated with coarse 

 tubuli. 



Sherbornina atkinsoni, gen. et.sp. nov. (Plate 32.) 



Description of Species. — Test discoidal, thin, complanate. Median area 

 depressed. Texture subtranslucent. Surface faintly showing the annular 

 series of the median layer with the crenulations of the superimposed spatulate 

 chambered layer on either side. A thin median horizontal section shows the 

 commencing series as a discorbine shell of about 7 chambers, followed by 

 4 imperfectly annulate series, the last two almost completely ring-like and 

 embracing the earlier series. Primordial chamber spherical, measuring 58 fi 

 in diameter ; chambers 2, 3, and 4 subglobular, 5-9 sublimate, 10 and 11 

 subannulate and of equal width throughout *. Chamberlets of superficial 

 layers spatulate and squamosely arranged. Diameter of test in holotype 

 1-9 mm. Thickness of test on periphery '25 mm. Thickness in median 

 area *09 mm. Diameter of another specimen 2"3 mm. 



Relationships. — This very remarkable form represents for the Rotaliidre 

 the cycloclypeine annulate multichambered character combined with the 

 lepidocycline spatulate-chambered type found in the Nummulinidfe. But 

 instead of the lepidocycline character being found in the median layer, it is 

 here, strangely -enough, found superimposed on the cycloclypeine. median 

 series, to form a complex unrecognized in the Orbitoidinse. This structure 

 of both median and external layers is merely isomorphoas with the Cyclo- 

 clypeus and Lepidocyclina groups, as proved by the commencing series, which 

 is distinctly rotaliue, and especially discorbine. 



The true relationship of this generic type lies with the planorbuline group, 

 of which a remarkable and allied generic type, Cyeloloculina, has been 

 described by Messrs. Heron- Allen and Earland t. The present specimens 

 show the same stages of development for the median series of chambers — the 

 discorbine, the pavonine, and the annulate. As in Cyeloloculina, the tubuli 

 in Sherbornina are fairly coarse perforations, and the " deposit of shell- 

 substance between the tubuli" noted by Heron-Allen and Earlaud in 

 Cyeloloculina appear to have developed in the present form into small scale- 

 like chamberlets forming the external layers, besides which there is also the 

 crenulate and warty appeai - ance of the surface seen also in Cyeloloculina. As 

 in Cyeloloculina, Sherbornina has no distinct apertural orifice beyond the 

 openings on the face and periphery leading through the coarse tubuli lo 

 the chamberlets. 



* In this character Sherbornina atkinsoni resembles Cyeloloculina annulata rather than 

 C. polygyra of Heron-Allen and Earland. See postea and Journ. Rov. Micr. Soc. 1908, 

 pp. 536 and 538. 



t Journ. Roy. Micr. Soc. 1908, pp. 529-543, pi. xii. 



