DISTRIBUTION IN TIME. 171 



Fossik rrferrrd fo ilie llydroida on inmifficicnt (/ronnds. — The genus Oldlunmn had heeii 

 founded by Edward Forbes ' for the reception of certain enigmatical inijjressions which occur as 

 alraost the sole evidence of life in rocks of the Cambrian age. They are not only absolutely 

 special to this period, but are extremely limited in their geographical di.-itribution, having been 

 hitherto found only in a narrow area composed of these rocks in the counties of AVickiow and 

 Dublin. 



Tliev present two well-marked modifications of form. In one of these [Oldliaiiiia nnfiqua) 

 there is a distinct stem, which gives off, at short intervals on alternate sides, fan-shaped clusters 

 of somewhat dichotomously divided branches. In the other form {Oldhawia radiata) the stem 

 is absent, and the branches radiate from a common centre. 



The branches present an obscurely moniliform or nodulose appearance, which has been 

 supposed to indicate the remains of hydrothecse, and the fossil has accordingly been referred to 

 the Hydroida, with the Sertularia argentea as its nearest living representative. Oval-shaped 

 bodies have, moreover, been described as present on the branches in some rare instances, and 

 in these it is believed that we have the remains of gonangia." 



1 must, however, confess my inability to recognise hydroid characters in these obscure 

 impressions. The structure which has been taken for hydrothecae is never so well marked as to 

 justify this interpretation ; and though I have examined a great number of specimens, I have 

 never met with anything which can be regarded as gonangia. 



Whatever be the nature of Oldhamia, then, 1 am not prepared to place it among the 

 Hydroida. Forbes believed that its affinities must be sought for among the Tolyzoa, and this 

 view has at least as much in its favour as the other, while that which would regard Oldhamia as 

 a vegetable impression seems as tenable as either.^ Indeed, there are some facts which seem to 

 militate even against its organic origin, such as the undoubted extension observable, in many 

 specimens, of the impression through numerous successive laminae of the bed in which it occurs. 



Under the name of Corynoides calicularis Dr. Nicholson has described certain bodies which 

 he has found associated with graptolites in the Silurian shales of Dumfriesshire.* They are 

 small, flattened, narrow, wedge-shaped bodies, from one third to a half an inch in length, and 

 measuring about half a line in diameter at their broader end, from which a few short, irregular 

 processes diverge. Towards the opposite end they taper away to a fine point, or, according to 

 Dr. Nicholson, they sometimes terminate here in a double point. In the specimens examined by 

 myself, however, this double termination was not observed. They certainly never show any 

 evidence of attachment. Dr. Nicholson refers them to the tubularian hydroids, and finds tlieir 

 nearest ally in the living genus Corymorpha. 



^ Edward Foibes, "On Oldhamia, a New Genus of Silurian Fossils," ' Jouru. Geol. Soc. of 

 Dublin,' 1848. 



- See J. Kiunahan in ' Trans. Roy. Irish Acad.,' 1859, p. 547. Mr. Kinualian's paper contains 

 the best account we possess of Oldhamia, and is illustrated with excellent and cliaracteristic figures. 

 Under the name of O. discreta he describes a third form, which, however, is Iiardly distinct enough to 

 be accepted as a separate species. He strongly advocates the hydroid nature of the fossil, comparing 

 it to the living Scrlulaiia ari/entea. 



' Schimper (' Traite de Paleontologie vegetale,' 1869) regards Oldhumia as a plant, and places it 

 among the KulUpores. 



* Nicholson, in 'Geological ^Magazine' for 1867. vol. iv, p. 108, pi. vii, figs. 9 — 11. 



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