36 NORTH AMERICAN INDEX FOSSILS. 



ten feet (Beatticea). The base is generally covered by a con- 

 centrically wrinkled calcareous crust or epitheca. In structure 

 these bodies recall the hydrophyton of Hydractinia as described 

 above, consisting of numerous concentric undulating calcareous 

 laminae, separated by interspaces, and supported by radial pillars. 

 Both laminae and supporting pillars are traversed in most cases by 

 minute canals, and in some types vertical " zobidal tubes " with 

 tabulae occur, as in Millepora. The surfaces of the laminae are 

 marked by numerous pores, the openings of canals, and by 

 tubercles, blunt rounded prominences or " mamelons," or blunt 

 spines, and shallow furrows radiating from a center {Astrorhizce). 

 In some types [Actinostromd) the laminae are composed of a net- 

 work of calcareous rods disposed in a horizontal series. In some 

 cases the horizontal and vertical elements are so fused as to form 

 a dense reticulated tissue, when the separate components are with 

 difficulty distinguishable [Strom atopord). Frequently the hori- 

 zontal laminae are combined into strata or " latilaminae " of some 

 thickness, separated from each other by a slight interspace. 



Several species of Stromatoporoids encrust cylindrical corals 

 (Aulopora, Syringopora, Ceratopora, etc.) which become com- 

 pletely immersed in the Stromatoporoid, opening only on the sur- 

 face in circular orifices. These orifices were formerly thought to 

 be a structural part of the Stromatoporoid and the name Cauno- 

 pora was applied to these types. Similar commensalism occurs in 



some Bryozoa. 



Literature. 



1866. Winchell, Alexander. On the structure and affinities of the 

 Stromatoporoids. Proc. Amer. Assoc. Adv. Science, 1866, p. 91. 



1873. Hall, James, and Whitfield, R. P. Description of new 

 species of fossils. 23d Ann. Report N. Y. State Cabinet, pp. 226-228, 

 pi. 9. 



1874. Nicholson, H. A. Palaeontology of the Province of Ontario. 



1875. Palaeontology of Ohio, Vol. II. 



1878. Nicholson & Murie. The minute structure of the skeleton of 

 Stromatopora and its allies. Journ. Linn. Soc, Vol. 14. 



1878. Quenstedt. Petrefacten Kunde Deutschlands. Schwamme, 

 pi. 141 and 142. 



1884. Spencer, J. W. Stromatopoids. Bull. Mus. University of 

 State of Missouri, 1, 43-52. 



1886. Nicholson, H. A. On some new or imperfectly described spe- 

 cies of Stromatoporoids. Ann. and Mag. of Nat. Hist., Ser. 5, Vol. 

 17, p. 225 j Vol. 18, p. 8, Vol. 19, p. 1. 



