Diy MOLLUSCOIDEA—BRYOZOA SUB-KINGDOM V 
Jloors of successive layers. Zowcial covers with a small, usually sub-central orifice. Mon- 
ticules or maculae (containing cells differing from the average in size, or in having their 
apertures elevated) regularly distributed over the surface. 
Family 1. Monticuliporidae. Nicholson (emend. Ulrich). 
Zoaria massive, discoid or lamellar, ramose or bifoliate. Zowcial apertures polygonal, 
rounded, or wrregularly petaloid.  Mesopores occasionally wanting, in other cases numerous, 
angular, and crossed by crowded dia- 
phragms. Acanthopores abundant, 
usually small.  Cystiphragms always 
present in the mature region. Ordo- 
vician to (?) Devonian. 
The incomplete, curved, transverse 
partitions, termed cystiphragms by 
Ulrich, are the principal peculiarity of 
this family. It is possible that they 
represent ovicells, but their significance 
can only be conjectured. 
Monticulipora, dOrb. (Fig. 449). 
ae Sine bi _. Zoaria massive, lobate, or lamellate, 
tice Ci) and’ tangential (B) sections, 14), (after Ulrich, enerusting or free. Surface with 
monticules or plain. Zoccia poly- 
gonal, mostly thin-walled. Mesopores very few or absent. Acanthopores more or 
less numerous, small. Ordovician, (?) Devonian. 
Atactoporella, Ulrich (Fig. 450). Zoaria generally encrusting, rarely lobate or 
sub-ramose. Zocecia with very thin inflated walls, the apertures irregularly petaloid. 

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Fic. 450. 
Atactoporella typicalis, Ulr. Black River Group; Minnesota. Surface (4), tangential (4), and vertical (0) 
sections, 14/; (after Ulrich). 
Mesopores numerous, frequently isolating the zocecia, largely filled by a secondary 
deposit. Ordovician. 
Peronopora, Nich. (emend, Ulrich). Similar to the preceding, but zoaria bifoliate, 
and zocecial walls thicker, not inflected by the acanthopores, and more ring-like in 
transverse section. Ordovician. 

leads to the distal thickening of the zocecial tubes, namely, that of filling up spaces occasioned by 
the growth of tubes at the periphery, and by the change in direction of the tubes. 
Some of the tubes provisionally included under the term mesopores, like some of the acantho- 
pores, were doubtless occupied by specially modified polypides, which probably find their 
homologues in the avicularia and vibracula of recent Chilostomata. But many of the mesopores 
which are not invested by separate walls are to be regarded as mere interspaces between the 
zocecial tubes, and the purpose of their transverse partitions is to support the walls of the latter, 
as well as to assist intercommunication by means of the zoarial parenchymal cord. ] 
