American Paleozoic Bryozoa. 159 
A very peculiar group of species, which I shall, provisionally, also 
include in this genus, is found in the Monticulipora calceola, Miller 
and Dyer, M. clavacoidea, James (Nicholson), and an undescribed 
form. Though I have seen of the first at least a thousand specimens, 
and of the other two several hundred, I have not detected any evidence 
going to show that they have grown upon a foreign object. On the 
contrary, the special form of the central cavity, assumed. by each of 
the three species, is apparently due to the amount of curvature adopted 
by the tubes in their course from the point of gemmation to their 
apertures. In J. calceola the zoecial tubes are always quite strongly 
curved, in consequence of which the zoarium takes a turbinate form, 
the gradually enlarging internal cavity being enrolled in a plane, and 
often making nearly two complete volutions. In M,. clavacoidea, the 
tubes are straight, and proceed in almost a direct line to the surface. 
The form of the zoarium is therefore straight. In the undescribed 
species, which in 1880 I catalogued under the name of Chetetes con- 
cavus, the tubes curve but slightly. and the resulting form of the zo- 
arium is concavo-convex, the cavity which in M&M. calceola is strongly 
curved, and straight in M. clavacoidea, being represented in LZ. (?) con- 
cava, by an oval impression. ‘The internal structure of the cells and 
tube-walls of these species is, in all respects, very closely like that of 
L. ornata, and as such a structural similarity is of more importance 
than differences in the mode of growth, I have concluded, provision- 
ally, to unite them with Zeptotrypa. 
LEPTOTRYPA MINIMA, Nn. sp. (PI. VI., figs. 2, 2a and 20.) 
Zoarium consisting of very thin expansions adhering parasitically 
to the shells of a small species of Orthoceras, which are usually entire- 
ly covered by this delicate bryozoan. The surface shows at intervals 
of about .08 of an inch, abruptly elevated, small, conical monticules, 
two or three hundredths of an inch in diameter, and a little less in 
height. Their arrangement is often quite regular, in longitudinal 
and transverse or intersecting series. Their slopes are occupied by 
cells but slightly, if at all, larger than the average, while the summits 
often carry the apertures ofa variable number of much smaller cells, 
which, if the specimen be worn, may give the monticules a sub-solid 
appearance. Cells 45th to ;4,th of an inch in diameter, angular, 
and thin-walled. The spiniform tubuli are to be observed only in 
well-preserved examples, their position being indicated in such 
specimens by a slight elevation of the junction angles of the cells, 
above the general level of the cell-aperture, 
