BRYOZOA. 165 
Ptilodictya.| 
diagonal arrangement of the zocecia prevails throughout ; so that instead of narrow 
oblong-quadrate zocecial apertures along the center of the fronds, we have there, the 
same as on all other parts of the surface, rounded apertures situated in rhomboidal 
or hexagonal spaces. 
A subdivision of Escharopora is likewise possible, but in this case we make out 
three instead of two. In the first we have simple narrow zoaria, with the diagonal 
lines of zocecia extending without interruption, completely across the celluliferous 
faces. EH. recta and Ptilodictya falcifurmis N icholson, are good examples. In the 
second the zoaria are also simple, but wider, occasionally very large (e. g. Ptilodictya 
pavonia Orb.) and at regular intervals their surfaces exhibit clusters of large cells. 
The latter are commonly elevated into rounded or conical monticules. 
These two subdivisions though obvious enough and in the main indicative 
of natural relations, are nevertheless not entirely so, since they separate species like 
P. faleiformis Nicholson, and P. maculata, that most certainly are closely allied, and 
in practice sometimes difficult to distinguish even specifically. Again, we know 
forms, Escharopora (Ptilodictya) subrecta for instance, in which old examples, or may 
be they are entitled to the distinction of a variety, have one, two, or even three rows 
of monticules. On the other hand, I am fully convinced that in the young zoaria of 
the normally montiferous species, the monticules were, to say the least, a very 
inconspicuous feature compared to what they are on the fully matured zoaria 
(See footnote, ante p. 146.) 
The third subdivision includes the branching forms, So far as known, it is a 
natural grouping, and distinguished from the preceding by the branching of the 
zoaria, and parallel margins of the branches after the first or basal division. When 
the branches are wide, clusters of large cells and monticules are developed, but 
when they are narrow, the monticules are absent, and the large cells distributed 
along the non-poriferous edges. A subdivision of the branching forms is possible 
therefore precisely as in the simple species. 
In accordance with the above I offer the following amended definition of Ptilo- 
dictya and E'scharopora, and classification of species. 
Genus PTILODICTYA, Lonsdale, 1839. 
Zoaria bifoliate, simple, umbranched, lanceolate or falciform, terminating below 
in a solid, striated, pointed base, which originally fitted loosely in the centrally sit- 
uated cupshaped depression or socket of a small basal expansion, The latter grew 
fast to foreign bodies, is radially striated, and has small cell openings in the furrows 
between the striz. In very young examples, and in certain small species in which 
