GENUS ACICULARIA. 137 



margins of the old, so as to form an expanded disk, instead of being piled up one above 

 another, so as to form a cylinder, we should have the essential features of the simple type of 

 Orbitolitcs. — It may be conjectured, without much improbability, that Dactylopora is only a 

 single representative of a group whose various forms filled up the hiatus which at present 

 intervenes between itself and its nearest allies among the ordinary Foraminifera ; one such 

 link, indeed, we shall presently find in the comparatively simple type to be described under 

 the name Acicularia. 



199. Geographical and Geological Disfribution. — The recent forms oi Dacfi/lopora,\i\\\ch 

 all belong to the simple type D. enica, have not been met with anywhere save in the tropical 

 seas ; and the fossil forms are for the most part limited to the Eocene Tertiaries of the Paris 

 basin, though D. reticulata occurs in the Tertiaries of Italy and San Domingo. 



XII.— AcicuLAKiA (Plate XI, figs. 27—32). 



200. History. — The history of the genus Acicularia, first instituted by M. D'Archiac in 

 1843 ('Mem. Soc. Geol.,' tom. v, p. 366), is scarcely less singular than that q{ Bantylopora. 

 The genus was founded upon certain minute bodies detected by M. D'Archiac in the 

 " calcaire grossier," the narrowness, elongation, and occasional pointedness of one extremity 

 of which gave them some resemblance to a needle ; and the place assigned to this type by 

 its discoverer was among the composite organisms now distinguished as "polj'zoaries." In 

 this he was followed by Michelin, who repeated his figure of it ('Icon. Zooph.,' p. 176, pi. xlvi, 

 fig. 14) ; but M. D'Orbigny in the second volume of his ' Paleontologie Stratigraphique ' 

 published in 1850, ranked it in the Foraminiferous genus Ovidite-s, in close approximation 

 to Baciyhpora ; and in this determination he has been followed by Pictet (' Traite de Paleon- 

 tologie,' tom. iv, p. 484), who still, however, regards Acicularia as generically distinguished 

 from Ovidites proper by the pointedness of one of its extremities. By Bronn, on the other 

 hand (x, bd. i, p. 11, bd. iii, p. 166), it seems to be thought more probable that Aciadaria is 

 a peculiar form of sponge-spiculc ! We shall see that a careful microscopic examination of 

 this type affords adequate evidence that it is really Foraminiferous in character, but that its 

 true structure and its position in the series are altogether at variance with the ideas formed 

 of it by M. D'Orbigny ; since it is, like DactyJojjora, a composite organism made up by the 

 aggregation of a number of separate and independent chambers, being generically distin- 

 guished from it, however, by a difi^erent arrangement of those chambers. This fact has been 

 fully apprehended by Messrs. Parker and Rupert Jones, although they have not yet stated 

 it pubhcly ; and the description I give of the type is entirely based on the materials which 

 they have kindly placed at my disposal. 



201. External Characters. — The bodies to which the generic designation Acicularia 

 seems applicable, vary through a considerable range of forms ; being sometimes elongated 

 cyUnders gradually narrowing to a point at one end, but hollow through the greater part of 

 their length (Plate XI, figs. 27, 31, 32); sometimes flattened, but still hollow; and 



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