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FOSSILS OF DOUBTFUL AFFINITIES. 



Whitneyi, comprises organisms with a general resemblance to Archceo- 

 cyathus. The skeleton in this genus is also superficially very similar 

 to a simple Rugose Coral, being cup-shaped, turbinate, or cylindrical, 

 and either straight or curved (fig. 72 bis, a), the external surface 

 being sometimes concentrically annulated or vertically ribbed. There 

 is a deep internal cup (fig. 72 bis), the lining of which is perforated 



by numerous round or oval pores, 

 similar perforations, arranged in 

 vertical and horizontal rows, exist- 

 ing in the outer wall as well. The 

 space between the inner and outer 

 membranes is subdivided by a 

 number (from six to over one 

 hundred) of vertical radiating par- 

 titions (fig. 72, b), which have 

 a general resemblance to the 

 "septa" of the Madreporarian 

 Corals. These radiating septa 

 are usually perforated by rounded 

 apertures, which place contiguous 

 interseptal chambers in communi- 

 cation ; and they are commonly 

 connected together by irregular 

 transverse plates, resembling the 

 " dissepiments " of many corals. 

 The whole structure of the skele- 

 ton is thus more or less porous, 

 and a characteristic feature of the 

 genus is the presence of oblique 

 funnel-shaped canals leading into 

 the internal cup. As in the pre- 

 ceding genus, the skeleton is now calcareous, and microscopic sec- 

 tions show nothing which would prove that its constitution was at 

 any time essentially different, or that definite spicules existed. By 

 Mr Walcott, the fossil described by Mr Billings under the name of 

 Archceocyathus Minganensis has been referred to the genus Ethmo- 

 phyllum; but, as previously pointed out, the researches of Dr Hinde 

 have shown that this form was originally siliceous, with a spicular 

 skeleton, and that it is truly referable to the Lithistid Sponges. 



On the other hand, the fossils described by Billings from the 

 Cambrian rocks of Canada under the name of Archceocyathus atlan- 

 iicus would seem to differ considerably in structure from Archceocya- 

 thus proper (as based upon A. profundus, Bill.) ; and they have 

 recently been referred by Hinde to a new genus under the name of 

 Spirocyathus (apparently related to the Protopharetra of Bornemann). 



Fig. 72. — A, Longitudinal section of a small 

 specimen of Archceocyathus profundus, Bill., 

 slightly reduced in size, showing the reticu- 

 lated structure of the skeleton and the deep 

 cup at the summit ; b, Part of a transverse 

 section of the same, enlarged, showing that 

 the reticulated skeleton has a distinct radial 

 structure, the septa being connected by dissep- 

 iments. Cambrian, Labrador. (After Wal- 

 cott.) 



