Mr. H. J. Carter on the Fossil Foraminifera of Seinde. 459 



species, when compared with Pictet's figure (Traite de Paleonto- 

 logie, pi. 109. fig. 7), is distinctly that of the "perte du Rhone," 

 viz. Orbit olina lenticularis, Lam., under which name it is now 

 given ; and I cannot help thinking, with Messrs. Parker and 

 Jones (Ann. Nat. Hist. ser. 3. vol. vi. p. 36), that D'Orbigny's 

 Cijclolina must be intended for the flat and expanded variety (c) 

 of this fossil. Perhaps, also, his figures of it were taken, by 

 mistake, from Orbitolites ; but of this more hereafter. 



These fossils abound to such an extent at the place mentioned, 

 that a bed of stratified blue limestone upwards of 100 feet in 

 thickness is almost entirely composed of them ; while the pre- 

 sence of Ammonites and Cretacean fossils in the superincumbent 

 strata, also more or less richly charged with Orbitolina, proves 

 the whole to be of Cretacean age. 



Structure of Orbitolina lenticularis. — This fossil, like Conulites 

 Cooki, is composed of a cortical layer of chambers externally (^2), 

 which is more or less conical in shape, and more or less filled 

 internally with a columnar chamber-structure Q73). The cortical 

 layer here, however, is composed of concentric rings of chambers, 

 which begin in a central cell at the apex (c?4) and terminate at 

 the circumference of the base. Each annulus is divided into a 

 number of chambers with straight septa {da), faced superficially 

 by a reticular subseptal structure (d\), which extends into the 

 chambers a certain distance, but not throughout ; so that when 

 this facing or superficial reticulation is removed by acid, the 

 larger divisions beneath come into view (^2). 



The columnar structure, again, as in Conulites, is composed of 

 layers of compressed cells which more or less fill the cone, ac- 

 cording to the species (#3), and sometimes extend even beyond 

 the base so as to give this a convex surface. But there are no 

 opakc-white columns here, as in Conulites, and the granulations 

 on the patulous surface and convexity of the base respectively (e) 

 represent the ends of the columns of cells as in Orbitolites Man- 

 telli. While, therefore, Conulites is most like Orbitoides dispansa, 

 Orbitolina more resembles Orbitolites Mantelli; but Conulites 

 still differs from both in the great chamber-layer being helical, 

 instead of cyclical, as before stated. 



2. Orbitolina ? (PI. XVII. fig. 7, &c.).— Conical; base 



convex ; annular spaces wider and more reticulated than in the 

 foregoing species. Internal structure the same as that of O. 

 lenticularis. 



Largest size. — Height yf inch ; breadth at base, a little more. 



Loc. Valley of Kelat (Dr. Cook). 



Associates. — Alveolina elliptica, in white limestone ; the di- 

 minutive Foraminifera in the bed before mentioned, valley of 

 Kelat (Dr. Cook). 



