GENUS ORBITOLITES: GENERAL PLAN OF ORGANIZATION. 193 



in limine what are the opportunities I have enjoyed. The first and most important 

 of these was afforded me by the great abundance of Orbitolites of various sizes, 



from o to ( ), besides a vast multitude of fragments, in Mr. JUKES'S Australian 



dredgings ; besides which, Professor E. FORBES kindly put into my hands several spe- 

 cimens which had been taken in their living state by Mr. JUKES, from the marine 

 plants to which they were attached. All these I have carefully examined under the 

 microscope, so as to be able to make an exact determination of their external cha- 

 racters ; and of a large proportion I have made microscopic sections in various direc- 

 tions, that I might assure myself of every particular respecting their internal struc- 

 ture. When I had nearly exhausted these sources of information, I found a new and 

 most interesting series of specimens in Mr. CUMING'S Philippine collection; and by 

 the study of these I was enabled to test the validity of the conclusions, to which I had 

 been led by the examination of the Australian forms. The kindness of various friends 

 has further enabled me to examine specimens obtained from other widely-distant 

 localities, such as different parts of the Indian, Southern, and Pacific Oceans, the 

 Red Sea and the /Egean. And finally, I have had placed at my disposal, through 

 the instrumentality of Professor QUEKETT, several Orbitolites of various sizes and 

 ages, obtained on the shores of the Feejee Islands by the late Sir EVERARD HOME, in 

 which the animal substance occupying the interior had been preserved by the immer- 

 sion of the fresh specimens in spirits. 



9. Besides the existing forms, I have examined a large number of specimens of 

 Fossil Orbitolites, both from the Paris basin and from other localities ; and I have 

 instituted the same kind of minute comparison of these specimens, both with each 

 other and with the recent types, that I had previously made among the diversified 

 forms of the latter. 



10. Postponing, until adequate means shall have been supplied by the details of 

 their organization, to be presently given, the inquiry into the relationship of these 

 different forms (Sect. VI.), we shall proceed in the first place to consider the general 

 plan of organization of the Orbitolite, and then to study the variations to which this 

 is subject. 



II. General Plan of Organization. 



11. In studying the organization of the Orbitolite, we shall have recourse, on the 

 one hand, to the structural characters presented by the Animal, as displayed by the 

 fleshy residuum left after the decalcification of specimens in which it has been pre- 

 served ; and on the other, to the structural characters presented by the Shell, of 

 which some are visible on its surface, and without any preparation, whilst others 

 may be seen in thin specimens by transmitted light, but of which the greater part 

 can only be brought into view by thin sections taken in various directions, especially 

 horizontal or parallel to the surface, and vertical or perpendicular to the surface. 



