586 DE. CAEPENTEE'S EESEAECHES ON THE FOEAMINIFEEA. 



that have peopled the globe in the long succession of geological ages, and constitute its 

 present Fauna and Flora. 



[Note. I cannot bring to a conclusion this series of Researches, without on the one 

 hand gratefully acknowledging the liberality of the Council of the Royal Society, whose 

 assistance (from the Grant placed at their disposal by Government) has greatly aided 

 my investigations, by enabling me to have every important feature of form and struc- 

 ture accurately delineated under a sufficient magnifying power; and, on the other, 

 expressing my great obligation to the skill, intelligence, and patient assiduity of my 

 draughtsman, Mr. GEORGE WEST, by whose careful study of these organisms under 

 my direction I have been enabled to attain a much more thorough knowledge of their 

 nature than my own more limited time would have permitted me to acquire.] 



EXPLANATION OF THE PLATES. 



PLATE XVII. 



"With the exception of figs. 9 and 10, all the figures in this Plate 

 refer to Polystomella craticulata. 



Fig. 1. Polystomella craticulata, as viewed at a in its peripheral aspect, showing the 

 septal ridges and the intermediate rows of ' fossettes,' and, on the left of the 

 figure, the septal plane with the row of minute apertures along its inner mar- 

 gin ; at b is shown one of the lateral surfaces of the same shell, over the 

 central part of which the septal ridges are concealed by an exogenous deposit 

 that is irregularly dotted with punctations resembling the ' fossettes.' Mag- 

 nified 10 diameters. 



Fig. 2. Vertical section passing nearly through the umbilical axis, and laying open the 

 outer seven whorls, but passing by those of earlier formation, so as to bring into 

 view at e the external surface of the eighth (counting inwards). This figure 

 shows the gradual increase of the distance between the two lateral surfaces of the 

 successive whorls, of which those last formed do not invest the earlier, so that 

 the shell would be biconcave but for the large amount of solid exogenous deposit, 

 which not only occupies the umbilical region, but extends even to the last 

 whorl ; it also shows the continuity of this deposit with that outer portion of 

 the spiral lamina of each whorl which presents in section a plicated aspect; 

 and along the inner margin of each of the septa displayed in the section, ia 

 seen a row of minute septal pores, forming the only direct communication 

 between the chambers. The relations of the various parts of the canal-system 

 are well displayed in this section : <z, <z, the openings of the successive turns of 

 one of the spiral canals transversely divided ; b, b, the meridional canals, one 



