826 .MICROSCOPIC FORMS OF ANIMAL LIFE 



elongated extensions, which correspond to the ' alar prolongations ' 

 of other spirally growing Foraminifera, but which, instead of wrapping 

 round the preceding whorls, are prolonged in the direction of the 

 axis of the spire, those of each whorl projecting beyond those of the 

 preceding, so that the shell is elongated with every increase in its 

 diameter. Thus it appears that in its general plan of growth 

 Fusulina bears much the same relation to a symmetrical Rotaline or 

 Nummuline shell that Alveolina bears to Orbiculina ; and this view 

 of its affinities is fully confirmed by the Author's microscopic exami- 

 nation of the structure of its shell. For although the Fusulina 

 limestone of Russia has undergone a degree of metamorphism, 

 which so far obscures the tubulation of its component shells as to 

 prevent him from confidently affirming it, yet the appearances he 

 could distinguish were decidedly in its favour. And having since 

 received from Dr. C. A. White specimens from the Upper Coal 

 Measures of Iowa, U.S.A.. which are in a much more perfect state of 



FIG. 625. Section of Fusulina limestone. 



preservation, he is able to state with certainty, not only that Fusulina 

 is tubular, but that its tubulation is of the large coarse nature that 

 marks its affinity rather to the Rotaline than to the Nummuline 

 series. This type is of peculiar interest as having long been regarded 

 as the oldest form of Foraminifera which was known to have occurred 

 in sufficient abundance to form rocks by the aggregation of its in- 

 dividuals. It will be presently shown, however, that in point both 

 of antiquity and of importance it is far surpassed by another. 



Nummulmidae. All the most elaborately constructed, and the 

 greater part of the largest, of the ' vitreous ' Foraminifera belong to 

 the group of which the well-known Nummulite may be taken as the 

 representative. Various plans of growth prevail in the family ; 

 but its distinguishing characters consist in the completeness of the 

 wall that surrounds each segment of the body (the septa being 

 generally double instead of single), the density and fine porosity of 

 the shell-substance, and the presence of an ' intermediate skeleton/ 



