30 Messrs. W. K. Parker and T. R. Jones on the 



2. In the Indian seas is a similar little shell (about y^ inch 

 in diameter), which, however, exhibits four narrow curved cham- 

 bers (each forming nearly three-fourths of a circle), arranged 

 around a central, globular primordial cell, and composing the 

 low cone of the shell and its thin margin. In company with 

 this (which represents a varietal stage in advance of No. 1), we 

 find other specimens (about ^ inch in diameter) possessing as 

 many as ten semiannular chambers. This variety may be termed 

 Orbitolina semiannular is, 



3. From the Arctic, British, Mediterranean, and other seas we 

 have obtained some specimens of a very small Foraminifer (^ inch 

 diameter) having the shape of the one last described, and a very 

 similar arrangement of chambers. It has, however, a greater 

 complexity of structure, owing to the presence of numerous 

 secondary septa, transverse and short, in all but the first two or 

 three chambers. These superadded septa begin to appear in a 

 rudimentary form in the third or fourth chamber, on the inside 

 of the peripheral wall ; they never reach the umbilical border 

 of the annulus, and are irregular in their development, even in 

 the newest chambers, where they are sometimes thirty or more 

 in number. The base of the shell, or umbilical area, is traversed 

 by raised, sinuous, thread-like lines of shell-matter. In older 

 individuals these are succeeded by thicker and irregularly wavy 

 ridges, and ultimately nearly the whole of the basal surface is 

 masked by this exogenous growth, excepting a thin margin, 

 formed by the newest of the annular chambers, the transverse 

 septal lines of which are also limbate by superadded calcareous 

 matter. 



This shell, in its different stages of growth, has been well 

 described and illustrated, under the name of Patellina corrugata, 

 by Prof. Williamson (Monograph, p. 46, pi. 3. figs. 86-89) ; and 

 he notices the difficulty of placing this shell in its true relation 

 to other forms. 



Orbitolina (Patellina) corrugata is present in most sea-beds 

 that are rich with Foraminifers, from the littoral zone down to 

 500 fathoms ; but it does not occur in great abundance. 



4. In the shore-sands from Melbourne, Australia, rich with a 

 group of Foraminifers almost the exact counterpart of those of 

 Grignon, we find a small, subconical, finely perforated shell, 

 exceedingly like that last noticed (No. 3), but not unfrequently 

 attaining four times the size (^ inch). A difference, however, 

 exists. After the primordial chamber, there is usually only one 

 semilunar chamber, those succeeding being annular. The latter 

 are subdivided by short, transverse secondary septa, as in O. 

 corrugata, and the cells have a regular alternately concentric 

 arrangement. 



