548 DR. CARPENTER'S RESEARCHES ON THE FORAMINIFERA. 



however, serve only to give a general idea of the diversities of external conformation 

 which had presented themselves to him ; and notwithstanding their number and 

 variety, they do not include some of the most important among the protean shapes of 

 these bodies, nor do they throw any light upon their internal structure. 



80. The memoir of Professor EHRENBERG*, in which his group of Bryozoa was 

 originally constituted, contains the first recognition of the relationship between 

 Orbitolites (^[ 4) and Orbiculina ; of which the first had previously been ranked 

 among the Zoophytes; while the second (until the Rhizopodous nature of the whole 

 group of Foraminifera was made known by M. DUJARDIN in 1 835) had been associated 

 with the Cephalopods. Professor EHRENBERG'S description and figures of Orbiculina, 

 however, being just as inaccurate as I have shown those of Orbitolites to be (partly, 

 it seems likely, through his unacquaintance with the mode of making thin sections), 

 there is no occasion for me to make further reference to them. 



81. The excellent memoir of Professor WILLIAMSON-|~ " On the minute structure of 

 the Calcareous Shells of some recent species of Foraminifera," contains the first 

 approach to a correct description of the internal conformation of Orbiculina; and 

 the fact was fully recognized by him, that in advanced age, when the spiral type of 

 growth has given place to the cyclical, there is no other difference between the 

 structure of Orbitolites and that of Orbiculina, than that, which arises from the dis- 

 similarity of their earlier mode of development. Although I am satisfied that, as to 

 one or two points of minute structure, Professor WILLIAMSON has fallen into error, I 

 am disposed to attribute this to the want of a sufficient number of well-preserved 

 specimens for examination ; and for having it in my power to correct and extend his 

 description, I am chiefly indebted to Mr. HUGH CUMING, the specimens of this type 

 included in his Philippine collection being remarkable both for their high develop- 

 ment, and for their very beautiful state of preservation. 



82. The investigations of Professor WILLIAMSON are entirely unnoticed by M. 

 D'ORBIGNY in his latest classification of the Foraminifera;}:; Orbiculina being ranked 

 in the order Helicostegues, and being defined as follows, " Coquille nautiloide, com- 

 primee, forme'e de loges divise"es inteVieurement en compartiments regnliers, percees 

 de nornbreuses ouvertures en lignes longitudinales a 1'enroulement special ;" whilst 

 Orbitolites (his definition of which has been already cited, ^| 5) is placed in the order 

 Cyclostegues. The separation of the two genera by so wide an interval, is grounded, 

 therefore, on the assumption that the type of growth in Orbiculina is spiral, whilst 

 that of Orbitolites is cyclical. I have already shown that this assumption is incorrect 

 as regards Orbitolites, the early plan of whose growth is frequently spiral (^[ 54); and 

 I shall presently show that it is equally incorrect as regards Orbiculina, whose later 

 plan of growth is typically cyclical. And after having closely compared these and 



* Transactions of the Royal Academy of Berlin, 1839. 



f Transactions of the Microscopical Society, 1st series, vol. iii. p. 120. 



J Cours Elementaire de Paleontologie, torn. ii. Paris, 1852. 



