GEOLOGY AND PALEONTOLOGY OF THE CANAL ZONE. 191 



two facts SO well known to students of Madreporaria that they need 

 only to be mentioned. I can not be sure that all of the supposed 

 species recorded in this paper as vahd are really valid; and perhaps 

 m identifying specimens from one locaHty with species from other 

 localities I may not always have discriminated closely enough. I 

 am discussing close resemblances and minute differences, for^ these 

 are the basis of correlation within such regional limits as the borders 

 of the Gulf of Mexico and the Carribbean Sea, and the recognition 

 and proper evaluation of this kind of resemblances and differences 

 affect the reliability of the deductions as to age equivalence. I have 

 been as careful as I well could be, but I should not Hke to insist that 

 I am always right in these very refined matters of observation and 

 of^ inferences based on such refined observation. In order to mini- 

 mize error inherent in such work, I have tried not to rely on one 

 species, but on groups of species— for instance the species of OrU- 

 cella and of Goniopora in both the Emperador hmestone and the 

 AnguiUa formation— and I have utihzed the testimony of other 

 groups of organisms. 



Comparisons of faunas according to the percentages of species in 

 common may be very misleading. Faunas now living only a short 

 distance from each other may have nothing or ahnost nothing in 

 common. In order to illustrate this I am introducing a table of the 

 corals obtained in the Cocos-Keeling Islands by Dr. F. Wood Jones.* 

 Although the list has been published elsewhere, it is not very long 

 and strikingly illustrates f aunal phenomena that are of great geologic 

 importance. 



List of corals obtained by Dr. Wood Jones in Cocos-Keeling Islands and their habitat. 

 br.=branchiiig; frag.=fragile; msv.=massive; pl.=plate; incrust.=incrustmg. 



Name of species and growth-form. 



Habitat. 



Lagoon, 



Seriatopora angulata Klunzinger, delicately branched 



Pocillopora bulbosa Ehrenberg, br., form depends on environment.".".' 



damicornis (Esper), br., rather strong 



verrucosa (Ellis and Solander), stout br 



elegans Dana, strong br., aborted on sm'f '..'.'.'.'.'. 



eydouxi M. Edwards and Haime, br., rather strong. '.'.'.""".'. 



wootyowfsj Vaughan, br., rather strong 



Orbicella versipora (Lamarck), msv 



Cyphastrea microphthalma (Lamarck), msv .........'.'.'.'.'.'.. '. 



Echinopora lamcUosa (Esper), thin folia x 



Leptastrea purpurea (Dana), msv !"!'!""""!!I!"!II" 



hottae (M. Edwards and &iime')"msv"!!!!!![!!!i[ii'""l x 



immcrsa Klunzinger, msv [ 



Favia stelligera (Dana), msv x 



speciosa (Dana), msv. (dead specimen")!!"' 



Favites abdita (Ellis and Solander), msv ! 



melicerum (Ehrenberg), msv. (dead specimen)'!!!!! 



LeptoTia phrygia (Ellis and Solander), msv 



Hydnophora microconos (T^amarck), msv. (dead specimen) "! 



exesa (Pallas), lobate !!!!!! 



Barrier pools 



and barrier 



flat. 



Exposed 

 barrier. 



1 Vaughan, T. W., Some shoal-water corals from Murray Island (AustraUa), Cocos-Keeling Islands, 

 and Fanning Island, Carnegie Inst. Washington, Pub. 213, pp. 70-72, 1918. 



