46 OEGANIC DEPENDENCE AND DISEASE 



sites but distinguished by its habit of growth as well as 

 details of cell structure. It does not abound in species and 

 all that are known belong to the Middle and Lower De- 

 vonian faunas. The following are its known species : 



p. leuticnlare Hall; Helderbergian (New York). 



P. lentieulare var. lanrentinum Clarice; Grande Greve limestone 



(Gaspe). 



P. eonvexum Hall; Onondaga limestone (New York). LoAver 



P. problematicnim Goldfuss; Coblentzian (Western Europe). I Devonian. 



P. eonstantinopolitannm d'Arcliiac and Verncuil; Eoumeli 



shalesi (Turkey). 

 P. amazonicum Clarl:e ; Maeeuru sandstone (Brazil). 

 P. styloporum Eaton — Hamilton (New York, etc.) ; Middle Devonian. 



The combination of the Pleurodictyum with what was 

 long called a ''coiled central body" or a ''wormlike ob- 

 ject," actually the curved tube of a commensal worm, has 

 long been known from the internal casts preserved in the 

 sandy shales of the Coblentzian. 



The concurrence of the coral and its convoluted worm 

 has been noted in several of the species here mentioned, 

 but the varying degree of its frequency is instructive. Thus 

 in the earliest species, P. lentieulare, I have seen the worm 

 tube very rarely, after the examination of a considerable 

 number of examples; in the var. laurentinuin not at all; 

 never in the large species P. eonvexum Hall of the Onon- 

 daga limestone. The single published illustrations of P. 

 amazomcwn and P. constantinnpolitaviim show its presence 

 but enable one to form no conception of its prevalence. The 

 combination is frequent enough in P. problematicum to have 

 given rise to the specific name of the coral. The American 

 Middle Devonian P. styloporum has afforded the material 

 for most of the illustrations here given. Of this very com- 

 mon species in the calcareous shales of the Hamilton group 

 I have been able to examine critically a great many individ- 



1 The Eoumeli shales of Eoumeli-Hissar and elsewhere in the vicinity of 

 Constantinople are generally regarded as the Mediterranean equivalent of the 

 Coblentzian of the Ehineland. 



