354 



PROTOZOA. 



Although the zoological rank of Areheoeyatlms Calaihium and Rhah- 

 daria is not positively established, I shall retain them among the Protozoa 

 for the present, provisionally. 



Genus Archeocyathus. {Ante, p. 3.) 



Fig. 342. 



Fig. 342. — Archeocyathus Minganends. a, fragment of the cylindrical portion of a 

 silicilied specimen of this species ; 6, end view of the same specimen. 



Remarks. — The following are some additional details of the structure of 

 this remarkable genus. The general form, as exhibited by the three 

 species at present known, is that of an elongated hollow cone, or, rather, 

 a hollow cylinder, Avith one end narrowed to a point, the smaller extremity 

 being closed and more or less curved ; the larger end open. They thus 

 resemble certain large species of Zaphrentia or Ct/athophi/Uum, and, in 

 fact, from their form and septate structure were at first thought to be 

 corals. Some of the individuals appear to have attained a length of two 

 or three feet, with a diameter of three or four inches. All of the species 

 are transversely and more or less deeply marked by irregular annulations. 

 The structure consists of an inner, thin wall, or endotheca, lining the great 

 central cavity, — an outer wall, or epitheca, forming the rough external 

 surface and, between these, a system of radiating septa. The outer wall, 

 in two of the species, A. profundus and A. Min(/anensis, is perforated 



