XX.—The GenusDictyoconusand its Allies: A Review of the Group, together with a Description of Three New Species from the Lower Eocene Beds of Northern Baluchistan

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AbstractThe author recalls the various opinions which have been expressed as to the relationships of Blanckenhorn's genusDictyoconusto other foraminiferal types. He shows howDictyoconushas been affiliated to the generaLituola, Lituonella, andCoskinolinaby such authorities as Messrs Schlumberger, Douvillé, and Schubert in the past; but has since been dissociated from them by Professor Cushman in his recent monograph on the Foraminifera. The author then discusses the grounds for this dissociation, which seem to him to be inadequate; and he describes his discovery, in certain Lower Eocene beds of Northern Baluchistan, India, of numerous specimens ofDidyoconus, Coskinolina, andLituonella, mixed indiscriminately together within the same narrow limestone bands, and deceptively similar in external appearance. He describes the differences between these genera—differences which are confined to the peripheral portion of the test—and shows how sections of the three Indian forms reveal the closest agreement in their internal characters as a whole; their generic characters alone affording the means of distinguishing between them. He therefore regards these Indian forms as affording clear evidence of the close affiliation of these three genera. These Indian forms, which are the first representatives of their respective genera to be found so far east, are very similar to such western forms asDictyoconus egyptiensis(Chapman),Coskinolina liburnicaStache, andLituonella robertiSchlumberger and Douvillé; but they have individual peculiarities of their own, and so are described by the author as three new species.