418 



and for the natural classification of which there is consequently no 

 safe basis, the author has undertaken a careful study of some of its 

 chief typical forms, in order to elucidate (so far as may be pos- 

 sible) their history as living beings, and to determine the value of 

 the characters which they present to the systematist. In the pre- 

 sent memoir, he details the structure of one of the lowest of these 

 types, Orbitolites, with great minuteness ; his object having been, 

 not merely to present the results of his investigations, but also to 

 exhibit the method by which they have been attained ; that method 

 essentially consisting in the minute examination and comparison of 

 a large number of specimens. 



The Orbitolite has been chiefly known, until recently, through the 

 abundance of its fossil remains in the Eocene beds of the Paris 

 basin ; but the author, having been fortunate enough to obtain an 

 extensive series of recent specimens, chiefly from the coast of 

 Australia, has applied himself rather to these as his sources of in- 

 formation ; especially as the animals of some of them have been suf- 

 ficiently well preserved by immersion in spirits, to permit their cha- 

 racters to be well made out. 



As might have been anticipated from our knowledge of their con- 

 geners, these animals belong to the Rhizopodous type ; the soft body 

 consisting of sarcode, without digestive cavity or organs of any kind ; 

 and being made up of a number of segments, equal and similar to 

 each other, which are arranged in concentric zones round a central 

 nucleus. This body is invested by a calcareous shell, in the sub- 

 stance of which no minute structure can be discerned, but which 

 has the form of a circular disk, marked on the surface by concentric 

 zones of closed cells, and having minute pores at the margin. 

 Starting from the central nucleus, which consists of a pear-shaped 

 mass of sarcode, nearly surrounded by a larger mass connected with 

 it by a peduncle, the development of the Orbitolite may take place 

 either upon a simple, or upon a complex type. In the former (which 

 is indicated by the circular or oval form of the cells which show 

 themselves at the surfaces of the disk, and by the singleness of the 

 row of marginal pores), each zone consists of but a single layer of 

 segments, connected together by a single annular stolon of sarcode ; 

 and the nucleus is connected with the first zone, and each zone with 

 that which surrounds it, by radiating peduncles proceeding from this 



