46 
ORGANIC 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. lenticulare Hall; ITelderbergian (New York). 
P. lenticulare var. laurentinum Clarice ; Grande Greve limestone 
(Gaspe) . 
P. convexum Hall; Onondaga limestone (New York). Lower 
P. problematicum Goldfuss ; Coblentzian (Western Europe). Devonian. 
P. constantinopolitanum d’Archiac and V erneuil ; Roumeli 
shalesi ( Turkey ) . 
P. amazonicum Clarice ; Maecuru 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. lenticulare, I have seen the worm 
tube very rarely, after the examination of a considerable 
number of examples ; in the var. laurentinum not at all ; 
never in the large species P. convexum Hall of the Onon- 
daga limestone. The single published illustrations of P. 
amazonicum and P. constantinopolitanum 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- 
i The Roumeli shales of Roumeli-Hissar and elsewhere in the vicinity of 
Constantinople are generally regarded as the Mediterranean equivalent of the 
Coblentzian of the Rhineland. 
