THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 66. JUNE 1853. 



XXXVIII. — Description of Orbitolites Malabarica {H. J. C), 

 illustrative of the Spiral and not Concentric Arrangement of 

 Chambers in lyOrbigny's Order Cyclostegues. By H. J, 

 Carter, Esq., Assistant Surgeon, Bombay Establishment. 



[With a Plate.] 

 Orbitolites Malabanca (H. J. C). 

 Description. — Free, discoidal, thin, plane or slightly concave on 

 one side and convex on the other, smooth; presenting spiral 

 lines on the surface extending from the centre to the circum- 

 ference. Margin thick, round, rugoso-reticulate longitudinally, 

 with one or more pores in the interstices ; each poi-e being sur- 

 rounded by a raised rim or border. Size, l-30th of an inch 

 thick at the circumference ; 7 to 8-15iths of an inch in diameter 

 (Plate XVI. B. figs. I & 3). 



Internal Structure. — Composed of several layers of chambers, 

 which are formed of as many turns of an inclined plane in a 

 vertical spire ; covered externally by a thin incrustation, through 

 which the chambers may be seen with a magnifying glass of low 

 power. Chambers arranged in continuous spii'al rows extending 

 from the centre to the circumference, and increasing in number 

 outwards (fig. 2) ; alternate in adjoining rows, small in the centre, 

 largest towards the circumference, and in the superficial layer 

 on both sides, where they are oblong or ovoid vertically (fig. 4) ; 

 each presenting two round apertures communicating with the 

 next outer and inner chambers ; the outer aperture of the ex- 

 ternal row opening on the margin (fig. 3). Septa straight (and 

 being perpendicular to the, and alternate in adjoining, rows of 

 chambers), forming broken spiral lines running in the opposite 

 direction to them, so as to present the linear appearance seen on 

 the case of an engine-turned watch (fig. 2) ; but with the ex- 

 ception, that in the former the hues increase in number outwards 



Ann. £f Mag. N. Hist. Ser. 2. Vol xi. 28 



