with Observations on their Internal Structure. 175 



minute and confusedly arranged in the centre ; in Orbitoides they 

 are as large in the centre as at any other part and distinctly 

 arranged. All this, while it tends to separate Orbitoides Man- 

 telli, D'Orb.j from Lycophris dispansus, which is a type of the 

 genus Orbitoides, approximates it just as much more to Orbito- 

 lites ; hence my reasons for changing its name. 



The subgranular or tuberculated form which this species, as 

 well as Lycophris dispansus, presents externally, arises from the 

 extremities of the columns of compressed cells projecting above 

 the surface, increased sometimes, probably, by the intercellular 

 substance having been worn or dissolved away ; but this is not 

 the case towards the circumference, on account of the columns 

 being shorter, more vertical, and therefore nearer together, which 

 of course renders the intercellular space smaller. 



The septa seen in a vertical section of the central plane con- 

 sist of opake matter which surrounds the columns, and as the 

 latter end more or less in pointed extremities upon an imaginary 

 central plane, we often see those of the opposite side interknitting 

 with them, and the chambers of the centre of the plane assuming 

 a triangular shape (fig. 39) ; sometimes they are quadrangular, 

 and the septa continuous across the plane (fig. 38) ; at others they 

 are oblong vertically and curved a little outwards, like the septa 

 seen in a vertical section of the central plane of Nummulites, 

 which is their common form towards the circumference (fig. 37) ; 

 while, just as often, the central plane is composed of two or 

 three layers of spheroidal cells entire (fig. 36) ; from which I am 

 inclined to infer, that where the other forms appear, it is merely 

 from the cells running into each other vertically, and their pa- 

 rietes in this direction disappearing partially or altogether. In 

 examining a vertical section of this plane, we frequently observe 

 that every other space is a septum and not a cell ; this is owing 

 to the cells being arranged alternately in adjoining rows. 



2. Orbitolites ? Equilateral or inequilateral, discoidal, 



patulous, more or less wavy, gradually diminishing in thickness 

 from the centre, which projects a little above the general sur- 

 face, to the margin, which is thin, though more or less obtuse at 

 the edge. In other respects the structure of this is the same as 

 that of the last species described. Diameter of largest specimens 

 2 inches; thickness 3-24ths of an inch (figs. 40, 41). 



Loc. Scinde. 



Obs. The great points of difference between this and the last 

 species are, that it is not abruptly prominent in the centre, and 

 diminishes gradually to the margin. It also attains a far larger 

 size ; and, as Dr. Carpenter has remarked, he. cit., sometimes 

 " seems, instead of being a circumscribed disk," to have spread 



