﻿ZOOLOGICAL CONSIDERATIONS. 



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of Carboniferous or Permian age, the earliest known representatives of the family being 

 the Nubecularice of theTriassic and the JSpiroloculina of the Lower Liassic clays. But the 

 entire absence of these two families is counterbalanced by the comparatively large represen- 

 tation of the second on the list, and some of the most noteworthy facts elicited in the 

 course of these investigations are in connection with the history of the arenaceous and 

 sub-arenaceous types constituting the Lituolida. 



First in point of order stands the genus Saccammina, the only true rock-builder 

 (using the term as it might be applied to Fusulina or Nummulina) amongst the British 

 Carboniferous Foraminifera — structurally a most simple organism, standing apart from the 

 rest of the group, interesting to the geologist from its stratigraphical limitations, and to 

 the zoologist for its sudden disappearance with the Carboniferous period, and its 

 reappearance in a new form as a Post-pliocene fossil, or living in the deep water of our 

 northern seas. The three prominent genera of Lituolida} namely, Lituola, Trochammina, 

 and Valvulina, all appear in great strength, together with Endothyra, an essentially 

 Carboniferous type, hitherto but little studied. 



Lituola (proper) is represented by large rough examples both of its nautiloid and 

 crozier-shaped varieties, and the non-labyrinthic Haplophragmium by a single small and 

 delicate variety. 



Of Trochammina there are no less than nine distinct modifications, mostly of the non- 

 septate division of the genus, one variety only showing any regular segmentation. But 

 the genus Valvulina obtains the most unexpected enlargement from the study of the 

 palaeozoic types. Ehrenberg many years ago figured a single species, first assigning it to 

 Textilaria, and afterwards instituting a new genus, Tetrataxis, for its reception ; but 

 this is only one of a long series of forms which further research has brought to light. 

 The mutual relations of these genera is best traced by the examination of recent specimens, 

 and under favorable conditions all of them may be found off our own shores. The 

 careful study of a large set of specimens obtained from dredgings taken on the west 

 coast of Scotland has clearly shown, as I have elsewhere stated, 2 that the three groups 

 form one unbroken series, in* which the supposed distinctive characters of the genera 

 become confused and lost. This applies chiefly to the feebler and smaller varieties, and 

 need not affect the nomenclature in general use ; but it is important in a zoological sense, 

 and cannot be ignored in a scheme of classification. 



The genus Valvulina in an especial manner has been a stumbling-block to sys- 

 tematists. In its normal and best developed condition it presents a thick, arenaceous 



1 That is to say, of the Lituolida, as constituted by Dr. Carpenter and his colleagues before the family 

 had been enlarged by the discovery of certain recent deep-water types of Rhizopoda, the exact position of 

 which cannot yet be very positively affirmed — such as Astrorhiza, Botellina, Pilulina, Rhabdammina, 

 and others, some of them not even named as yet — none of which materially affect the present subject, 



2 'Annals and Mag. Nat. Hist.,' ser. 4, vol. vi, pp. 289, 290. See also Jones, Parker, and Kirkby, 

 ibid., vol. iv, p. 391 . 



