HYDROCORALLINES—STROMATOPOROIDEA. 37 



189 1. Same, part IV., do , ser. 6, Vol. 7, p. 309. 



1886-92. Nicholson, H. A. A monograph of the British Stromato- 



poroids. Palaeontographical Society monograph. 

 1894. Girty, G. H. Revision of the sponges and coelenterates of the 



Lower Helderberg Group of New York. 14th Ann. Rept. N. Y. State 



Geol., p. 289, Stromatoporoidea. 



Two keys are herewith given. The first is based on the micro- 

 scopic structure and requires thin sections. It is believed that by 

 its means most species may be traced to their proper genus. 

 The other is based on external characters and is given to make 

 possible field determination of the more important species of 

 " Stromatopora " in the old sense. It applies only to the species 

 described. 



I. Key to the Genera.* 



A. Calcareous tissue a meshwork of horizontal and vertical rectangular elements I. 



I. Structure an open meshwork, radial pillars distinct, horizontal laminae of cal- 

 careous anastomosing bars *. 



*. Radial pillars continuous through a number of laminae and interlaminar 



surfaces I. Actinostroma. 



*. Radial pillars discontinuous II. Clathrodictyon. 



I. Structure an open meshwork, radial pillars very large, horizontal elements thin 



irregular plates VII. Labechia. 



I. Structure a dense reticulate meshwork in tangential section, but more open in 



vertical section, the radial pillars distinguishable **. 



** Form spherical, massive or expanding aa. 



aa. Laminae bending upwards at regular intervals, forming a series of 

 vertical rod-like structures passing through the mass. 



f III. Stylodictyon . 

 aa. Laminae not bending upwards, short irregular zooidal tubes. 



IV. St7-omatoporella. 

 ** Form cylindrical and commonly branching, numerous well developed tab- 

 ulate zooidal tubes opening by circular pores V. Idiostroma. 



I. Structure a dense reticulate meshwork in both tangential and vertical sections, 



radial pillars generally not distinct ***. 



*** Structure reticulate, tabulate zooidal tubes well developed. 



VI. Stromatopora. 

 *** Structure very^dense, but vertical and horizontal elements distinguishable. 



VI. Syringostroma under Stromatopora. 



B. Calcareous tissue of concentric laminae, no vertical pillars II. 



II. With vertical tubes VII. Strom atoccerutm. 



II. Without vertical tubes VIII. Cryptozoon. 



C. Calcareous tissue a single layer covered with a basal epitheca and with numerous 



blunt tubercles on the surface IX. Labechia (young). 



D. Calcareous tissue a series of vesicles, form columnar X. Beatricea. 



* Based on microscopic structure. 



