96 
B. NATURAL HISTORY. 
The third species which I have ^described is Stromatopora nux. 
This occurs in moderate-sized spheroidal, sometimes contiguous and 
coalesced masses, formed, unlike the foregoing species, by accretions on 
all sides, and is often seen to be parasitic. The external surfaces of 
the layers are not pustulose. Masses occur from 2-J- to 12 centimetres, 
or 1 to 5 inches, in diameter. This species has also been recognized 
on Kelly’s Island. 
This is one of the species commonly referred, in this country, to 
S. concentrica, Goldf.; but I do not believe that species exists in 
America. S. nux differs from S. concentrica in the same manner that 
S. striatella does; but the latter is an Upper Silurian and a European 
species, and I should hesitate to unite it with S. nux. 
Lastly, a most unexpected and remarkable form has come under 
my observation, which I have described as S. ccespitosa. In general 
ensemble it looks like a large, cespitosely branching Cyathophylloid 
coral. The stems are externally in contact, or 15 to 25 millimetres 
apart. A longitudinal section shows the characteristic layers arching 
across the stem and resembling S. pustulifera in miniature. A trans¬ 
verse section exhibits a radiating structure, as in Gyathophyllidce ; but 
there is no outer wall or definite limitation to the structure, and the in¬ 
terior is completely filled with concentric circles of coralline substance, 
except a small perforation in the centre. The exterior is longitudi¬ 
nally vermicular-striate. Diameter of stem 4J to 7-J millimetres, or 
.18 to .30 inch. It occurs in masses from 6 to 9 decimetres, or 3 to 
4 feet in diameter. 
I think there can be no doubt that this species conforms to Stroma¬ 
topora , as defined by Goldfuss and McCoy. It possesses the concentric 
and reticulated layers of S. concentrica, pustulifera, and monticulifera. 
It is not enveloping, like the former, but presents an exaggerated con¬ 
dition of the unwalled pile of layers characterizing the two latter 
species. On the contrary, the ensemble is that' of a Cyathophylloid, 
and traces of radial, lamellar lines are actually present, producing ir¬ 
regular longitudinal striae on the exterior. It seems to possess, there-' 
fore, undoubted affinities with those genera of Gyathophyllidce in which 
the mural system is feebly developed, and the diaphragms and lamel¬ 
lae tolerably well represented. In short, it seems to exhibit a transition 
from Stromatopora proper to Gyathophyllidce. 
The affinities of this species with S. pustulifera and monticulifera 
