3 8 NORTH AMERICAN INDEX FOSSILS. 



II. Key to the Species of " Stromatopora " in the Old Sense Based 

 Chiefly on External Characters.* 



A. Form a flattened or undulating expansion, generally with a basal epitheca *. 



* Free or only attached at initial point a. 



a. Surface with mamelons aa. 



aa. Mamelons prominent ; astrorhizae present though inconspicuous, sur- 

 face granulate 9. S. granulata Dev. 



aa. Mamelons low, astrorhizae absent 1. S. expansa Dev. 



a. Surface sometimes undulated, with tubercles instead of mamelons ; no astro- 

 rhiza? bb. 



bb. Tubercles of two sizes, the larger with pores. 10. S. tuberculata Dev. 

 bb. Tubercles minute, in rows, with pores between rows. 



5. S. striatella Sil. 

 bb. Tubercles scattered, mesh work very coarse 7. S. cellulosa Dev. 



a. Surface without mamelons or tubercles cc 



cc. Astrorhizae well developed 2. S. fenestrata Dev. 



cc. Astrorhizae small 4. S. vesiculosa Sil. 



* Encrusting other fossils. Tubercles instead of mamelons ; astrorhizae present. 



II. S. incrustans Dev. 



B. Form massive, hemispheric or spherical **. 



** Divided into strata or latilaminae b. 



b. Surface with mamelons cc, 



cc. Astrorhizae well developed 14. S. monticuliferaDev. 



cc. Astrorhizae small I. 



1. Mamelons sharp and conical 3. S. nodulata T>ev . 



1. Mamelons low and rounded ; astrorhizae minute. 



17. S. centrota Lower Dev. 



b. Surface with pustules instead of mamelons dd. 



dd. Astrorhizae small 15. S. pusluliferaDzv. 



b. Surface without mamelons or pustules ec. 



ee. Astrorhiza present 2. 



2. Vertical section shows only dense tissue 16. S. densa Dev. 



2. Vertical section shows minute tabulate tubes traversing the entire 



stratum 13. S. antiqua Sil. 



ee. Astrorhiza absent 18. S. barre/ti Lower Dev. 



** Not divided into strata, or but imperfectly so c. 



c. Surface without true mamelons ff. 



ff. Astrorhiza absent 3. 



3. Surface finely granulated with pores between rows of granules. 



5. S. striatella Sil. 

 3. Surface with pustules, formed by the ends of large vertical rods. 



8. S. columnaris Dev. 

 3. Surface with pustules in regular diagonal lines, and large irreg- 

 ular nipple-like elevations 6. S. ostiolata Sil. 



c. Surface with conical mamelons, astrorhizae small 3. S. nodulata Dev. 



C. Form cylindrical or branching ***. 



*** Surface with prominent pointed tubercles d. 



d. Branches with rounded ends, surface porous 12. S. avspitosa Dev. 



*This is adapted only to the species here described. It does not include Stromato- 

 ccerium, Cryptozoon, Labechia or Beatricea. Endings become feminine. 



