CONTRIBUTIONS TO PALiEONTOLOGY. 



79 



SPIROPHYTON CAUDA-GALLI. 



Fucoides cauda-galli : Vanuxem, Geological Report Third District, p. 128. 



General form circular, often irregular, the outline undefined. The 

 ridges or fascicles, curving gently from the centre, are more ab- 

 ruptly bent towards the margin ; and being stronger near the 

 centre, have a fanciful resemblance to the feathers of a cock's 

 tail, from which the name has been given. 



This species is so extremely abundant, that it often covers large surfaces 

 of the rock ; and lying so closely together that the outlines are usually 

 destroyed, it is diffi-cult to procure good specimens, or those which show the 

 entire form of the frond. The larger discs often reach a diameter of more 

 than a foot ; but from the peculiar texture of the rock, the successive 

 volutions have not been traced. 



The specimens figured by Mr. Vanuxem illustrate the prevailing cha- 

 racteristics of the species on a small scale. 



Fig. 1. 



Fig. 1, illustrates the ordinary character an^ aspect of this fossil. 



