BRYOZOA. 157 
Pachydictya.] 
well preserved examples a thin peristome is clearly distinguishable, and, running 
lengthwise between the rows of apertures, a thin ridge raised considerably or only 
slightly above the level of the peristomes. The interspaces are always as wide as 
the zocecial apertures, and in many specimens nearly twice.as wide. One specimen 
preserves a few “closures”’ or zocecial covers. These are faintly convex, with a small 
rounded opening in the anterior half. 
Of internal characters, | shall mention, (1) the absence of interstitial vesicles 
between the primitive or prostrate cells of the zocecia ; (2) the contact of those por- 
tions of the zocecia with each other on all sides, resulting from the absence of the 
vesicles ; (3) the peculiar convex shape of the anterior or transverse partitions of the 
primitive cells; (4) the density and early beginning of the solid interstitial filling, 
and consequent indistinctness of the vesicles. Diaphragms are usually present, one 
or two in each tube. y 
Compared with other species, P. elegans is found to differ, externally, in its usu- 
ally wider and more rapidly branching zoarium, and flatter interspaces ; internally 
in the shape of the primitive cell and the earlier development of the intersititial 
vesicles. P. occidentalis is sufficiently distinguished by its mode of growth and its 
maculose surface, and P. fimbriata by its peculiar ruffled non-poriferous margin. 
Formation and locality.—This species is one of the commonest fossils of the Galena shales, having 
been found at perhaps every one of the numerous localities in the state where that horizon is exposed. 
Also at Decorah, Iowa. It occurs also in the lower layers of the overlying limestones, at Fountain, and 
several specimens have been collected from the Phylloporina corticosa horizon. Its wide geographical dis- 
tribution outside of the state has been mentioned already. 
Mus. Reg. Nos. 7607, 7609, 7616, 7619, 7623, 7632, 7639, 7643, 8027. 
Pacuypicotya pumILA Ulrich. 
PLATE X, FIGS. 1-4. 
Pachydictya pumila UtRicu. 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 186, fig. 11. 
Rhinidictya humilis Utricn, 1890. Jour. Cin. Soc. Nat. Hist., vol. xii, p. 185, fig. 10. 
Zoarium bifoliate, small, usually less than 1 cm. in height, growing rather 
irregularly. Branches from 1.0 to 1.5 mm., wide, generally bifurcating at intervals 
of from 2 to 4mm., but some fragments observed are undivided for a distance of 6 
or8mm. Zocecia in from three to six ranges, with four or five the average number 
shortly after bifurcations. The arrangement of their oval apertures is inclined to 
be rather irregular, though more or less longitudinal rows prevail in most cases. 
Over the basal parts of the zoarium this irregularity is apparent in a higher degree 
than in the distal portions. In the latter five to seven occur in 2 mm. longitu- 
dinally. The size of the apertures and the general appearance of the surface varies 
with age and other conditions. Nearly complete examples may show all the phases. 
