OERAMOPORIDiE. 19 
with each other. The growth may be free, discoid, lamellate, massive, or incrusting, the 
spongy basal layer may be absent, and the diaphragm may or may not occur. 
The various species of Ceramopora may be distinguished by external features that are 
more readily perceived b}^ a study of actual examples than by description. This peculiar 
aspect of the surface seems to be the result of the open mesopores, together with the irregu- 
larity of both zooecia and mesopores, and the prominent lunaria. 
Ceramopora imbricata Hall. 
PI. VI, figs. 1-10. 
Ceramopora imbricata Hall, Nat. Hist. New York, Pal. II, 1852, p. 169, pi. 40E, figs. la-i. 
Ceramopora imbricata Ulrich, Geol. Survey Illinois, VI 11, 1890, p. 463, pi. 39, figs. 1-lb. 
Ceramopora imbricata Grabau, Bull. New York State Mas., No. 4. r >, 1901, p. 163, fig. 58. 
Ulrich (op. cit.), has brought out the salient features of this species in the following 
description: 
Zoarium free, discoidal, plano-convex, under side sometimes slightly concave, from 5 to 15 mm. in 
diameter; thickness at center seldom exceeding 4 mm., usually only about 2 or 3 mm. No epitheca on 
the lower side. Lower or basal portion of zoarium composed of a cellular or spongy tissue, from which 
the zooecia grow out more or less obliquely. At the depressed center of the zoarium the zocecia are 
nearly direct, but toward the margin they gradually become more and more oblique. Zocecia com- 
pressed tubular, being long oval in transverse section. Apertures imbricating, arranged in multiply- 
ing radial series, all facing away from the center, triangular or oval in outline, 0.5 to 0.7 mm. in their 
long diameter. Intercellular space occupied by irregularly flexuous rows of mesopores, variously 
shaped, short. Zocecial tubes and mesopores communicate rather freely by means of perforations in 
the walls. Besides, the walls have that granular structure which is supposed to indicate originally 
minutely porous condition. Lunarium small, yet well marked. No diaphragms developed. 
To the above may be added that growth in this species commences parasitically on small 
foreign objects, crinoid stems being usually selected. As new tubes are added, the free disk- 
shaped zoarium results by growth beyond the object originally incrustcd. The latter in 
some specimens is still preserved but more frequently is represented only by the cicatrix of 
attachment. Measuring along one of the rows radiating from a macula, three zooecia are 
usually found in a distance of 2 mm. A young or even average specimen is made up of a 
central macula from which the zooecia radiate toward the growing edge, but larger exam- 
ples exhibit several macula?. 
The discoid growth, spongy basal layer, and the conspicuous maculae with the radiating, 
oblique, imbricated zocecia are characters by which this species can readily be distinguished 
not only from all associated bryozoa but also from other species of Ceramopora. Aleso- 
trypa nummiformis has a similar discoid method of growth but the much smaller zooecia, 
absence of a luna>rium and the epithecated under surface are external characters which will 
distinguish it at once. 
Occurrence. — Not uncommon in the Rochester shale at Rochester, Lewiston, and Lock- 
port, N. Y., and in the same formation at Thorold and Grimsby, Ontaiio. Rather abun- 
dant in the Osgood beds at Osgood, Ind. 
Catalogue numbers, 35464, 35465, 35466, 43280, U. S. National Museum. 
Ceramopora niagarensis n. sp. 
PI. VI. figs. 11-13. 
/zoarium explanate, at first attached to foreign bodies, then becoming free and provided 
with an epitheca; by the superposition of several layers, rounded or irregular lumps 2 to 4 
cm. in diameter may result. Thickness of the individual layers of a zoarium varying 
from 1 to 2 mm. Celluliferous surface tough on account of the prominent lunaria and 
exhibiting well-marked maculae composed of open mesopores. Zooecial apertures nearly 
direct, ovate, three in 2 mm., rather regularly arranged about the macuhe. Lunarium 
strongly elevated and well developed, occupying the posterior half of the zooecial aperture. 
Mesopores, as usual in the genus, open at the surface and variable in size, shape, and num- 
ber, but commonly about two to a zocecium. 
