i«3 



CHAPTER XII. 



FOSSILS OF DOUBTFUL AFFINITIES. 



I. ARCHiEOCYATHIN^E. 



The lowest Cambrian strata (" Oleiiellus Beds ") of North America, 

 Spain, and Sardinia have yielded the remains of a number of re- 

 markable organisms, which may be collectively spoken of as the 

 Archceocyathince, but which cannot at present be definitely referred 

 to their place in the zoological series. The three genera which may 

 be regarded as typical of this group of organisms are Archceocyathus, 

 Ethmophyllum, and Spirocyathus, and the characters of these may 

 be briefly treated of here. 



There is some difficulty in determining for which of the species 

 described by Mr Billings under the name of Archceocyathus this 

 generic title should be retained. If, however, we follow Hinde, 

 and accept Archceocyathus profundus, Bill., as the type of the genus, 

 we have to deal with elongated, turbinate, more or less curved 

 fossils, sometimes more than a foot in length, with a diameter of 

 from two to four inches, having a general resemblance to such 

 Rugose Corals as the simple species of Cyathophyttum. The conical 

 skeleton is hollow, with a deep, cup-shaped internal cavity, the sur- 

 face of which shows radiating ridges, and is bounded by a thin 

 inner wall (fig. 72, a). Both the inner and outer walls are per- 

 forated by pores, and the space between the two is traversed by 

 numerous vertical septa, which are in turn connected by delicate 

 dissepiments, giving the general structure a vesicular character (fig. 

 72, b). Archceocyathus profundus stems to have been undoubtedly 

 calcareous in its original constitution, and there is no evidence that 

 its skeleton was at any time composed of spicules. The original 

 specimens were obtained in the Cambrian strata of the Straits of 

 Belle Isle, Labrador. 



The genus Ethmophyllum^ as based upon the fossils described by 

 Mr Meek from the Cambrian strata of Nevada under the name of E. 



