BRYOZOA. 153 
Pachydictya.] 
vals; angle of bifureation unusually wide. Non-poriferous margin very wide, 
extremely thin and sharp, and wavy or ruftled; its surface is obliquely striated, 
the striz really rows of minute hollow papille, which communicate with the hori- 
zontal median tubuli between the mesial lamine. Zocecia in from seven to twelve 
ranges, the usual number ten or eleven; their apertures elliptical, usually a little 
wider than the transverse interspaces, and longer than the end spaces. In the five, 
six, or seven central rows the apertures are arranged in regular alternating or sub- 
alternating longitudinal series, in which thirteen or fourteen occur in 5 mm.; meas- 
uring transversely six rows take up a space of 1.5mm. wide. The one to three 
marginal rows are not so regular in their arrangement, they being, besides, appre- 
ciably larger and separated by wider interspaces, while their long diameter is, usually 
at least, directed somewhat obliquely outward. 
On plate IX, fig. 13 represents part of a tangential section, showing, at the top, 
the primitive or prostrate portion of the zowcia, and mesial lamin with horizontal 
tubuli; along the right side, the wide non-celluliferous border, which in thin sections 
is irregularly outlined and incomplete, because of its “ruffled” character ; and in the 
lower left-hand fourth, the zocecia and interspaces as they appear just beneath the 
surface. In the last portion of the figure the chief feature to be pointed out is the 
unusual clearness and thickness of the ring-like zocecial investment. Incommon with 
perhaps every species of this section of the genus, and many of section a, the longi- 
tudinal arrangement of the zocecia between distinct lines, either straight or flexu- 
ous, and proving on closer inspection to be series of minute pores, prevails in the 
central rows through all stages, saving, perhaps, the last in very old examples. 
Good examples of this species cannot be confounded with any other known to 
me, since the great width and wavy or ruffled character of the non-poriferous 
margin gives them a very striking and highly characteristic aspect. In most other 
respects the species resembles P. acuta Hall, sp., and its western varieties rather 
closely. It may be compared also with P. elegans and its described variety. In that 
species and variety the non-poriferous margin is also rather wide, but it is not wavy 
and the inter-apertural spaces are wider, especially those between the ends of the 
zocecial apertures, while the whole surface of the zoarium strikes one as more highly 
ornamental. Considerable differences are likewise to be noted in tangential sections 
as may be seen in comparing figuies 8 and 13 on plate IX. 
Formation and locality.—Rather common in the lower half of the Trenton shales at Minneapolis and 
St. Paul, Minnesota. It occurs also in the ‘‘ Pierce” limestone of Tennessee. 
Mus. Reg. Nos. 5950, 5951. 
