ZOOLOGICAL CONSIDERATIONS. 17 



two Belgian localities. As the recognition of these types at so early an epoch involves 

 consequences of considerable importance, extreme care has been taken in the verification 

 of the geological position of the rocks from which the specimens were obtained. Happily 

 confirmatory evidence of considerable weight is supplied by their lithological condition, 

 which under the microscope is almost exactly similar to that of the minute fossils of the 

 Fusulina-beds of some parts of Russia and North America, and there is really no room 

 to doubt that they are of Carboniferous age : but from a zoological point of view it would 

 be very satisfactory to meet with the same species under conditions more favorable to 

 the preservation of minute peculiarities of form and structure. The earliest occurrence 

 geologically of any member of this group, previously recorded, is that of Pulvinnlhia 

 cassiana (Giimbel) from the St. Cassian marls of the Alpine Trias, the earliest English 

 example being the closely allied Pulvinnlina el cyans (d'Orb.), found by Messrs. Parker 

 and Jones in the Upper Triassic or Rhsctic Clay of Derbyshire. The Carboniferous 

 specimens are unfortunately not only few as to number, but very obscure in their morpho- 

 logical characters, but they are of interest as carrying the history of the Rotaline genera 

 into Palaeozoic times. 



The importance of the NUMMULINIDA as a family of Carboniferous Foraminifera rests 

 chiefly on the genus Fusulina, which holds a similar position in the later Palaeozoic fauna 

 to that occupied by Nummulina and its allies at the beginning of the Tertiary epoch. 

 As it is proposed that the genus Fusulina should form a subject for separate treat- 

 ment, the facts which have been gathered from its fresh study need not at present be 

 touched upon, though there is a great deal, especially in the characters of some of its less 

 familiar varieties, of much significance in its bearing on the morphology and development 

 of the Nummulite itself. 



But in addition to Fusulina, the family is represented by minute specimens of three 

 other genera, Arclicediscus, AmpMstegina, and Nummulina. The first of these, Archcediscus, 

 a type as rudimentary in its organization as is compatible with Nummuline structure, 

 makes perhaps the earliest appearance in point of time, and of the three it alone can be said 

 to be even moderately common or widely distributed. Amphistegina, regarded hitherto 

 as an essentially Tertiary and recent genus, is represented by one or two very minute 

 but quite characteristic specimens, whilst Nummulina has only been obtained as yet 

 from a circumscribed portion of the Belgian limestones. The absence of any known 

 data for the determination of the relative age of the Carboniferous beds, of areas 

 widely separated geographically, renders it impossible to draw zoological inferences with 

 precision, as to the succession of species in the upper palaeozoic rocks, and the Foraminifera 

 themselves are scarcely available for anything more than collateral evidence. 



From what has been said it will be gathered, that the principal points in the general 

 aspect of the Carboniferous and Permian Rhizopod-fauna are: 1st. That the prevalent 

 forms (except Fusulina} do not belong, in a strict sense, to either of the two suborders 



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