BRYOZOA. 253 
Prasopora lenticularis.] 
at intervals of about 3 mm., each a mm. or more in diameter. Surrounding these 
the surface is depressed to a variable degree, and occupied by angular zocecial 
apertures of comparatively large size and very few mesopores. The average diam- 
eter of these zocecia is about 0.28 mm. On the rounded ridges between the depres- 
sions the zocecial apertures are circular and smaller, averaging about 0.2 mm. in 
diameter; here they are also completely surrounded by a row of small mesopores. 
Internal characters: The tangential section figured on page 248 shows in the 
upper half one of the macule with the large zocecia surrounding it and occupying 
the depressed hexagonal surface spaces. Between these zocecia the mesopores are 
very few, but farther out, in spaces representing the ridges (lower third of figure), 
the mesopores usually completely isolate the, here also smaller, zocecia from each 
other. Acanthopores are wanting. 
In vertical sections (fig. 15c) the macule appear as numerous, small, subequal, 
closely tabulated tubes. One or two similar mesopores occur between many of the 
zocecia in the inter-macular spaces. In the zocecial tubes the transverse partitions 
are quite different. The appearance of the cystiphragms depends upon the direction 
in which the section passes through them. When this is at right angles they appear 
(see the central tube of the three shown in the figure) as narrow loops projecting 
inward from the walls. Sometimes a complete diaphragm passes between each pair. 
A variety of appearances, some of them shown in the figure, result when the section 
passes through the cystiphragms at other than a right angle. 
This species is readily distinguished from its associate, P. insularis Ulrich, as well 
as from all the other species of the genus known to me, by the division of the surface 
into subhexagonal depressed spaces. The zoarium is also unusually thin, while the 
internal structure is peculiar enough to be distinguished at once, even from its 
nearest allies, P. affinis Foord, and P. selwyni Nicholson. Still, I am not fully satis- 
fied that the form is in all cases to be distinguished specifically from P. affinis, small 
specimens of which have recently been found associated with it. 
Formation and locality.—Rather rare in the Galena shales at several localities in Goodhue county, 
Minnesota. The types of the species are from the equivalent Trenton limestone at Ottawa, Canada. 
Mus. Reg. No. 7625. 
PRASOPORA LENTICULARIS, ”. Sp. 
PLATE XVII, FIGS. 22-25, 
Zoarium small, lenticular, beginning its growth upon foreign bodies, as far as 
observed, about 12 mm. in diameter and 1 mm. thick. Zoccial apertures regularly 
arranged, oval, twelve or thirteen in 3 mm., each of the smaller or average size 
0.18 by 0.23 mm. In the clusters a few of the largest may attain a size of 0.35 by 
