272 



MOLLUSCOIDEA BRYOZOA 



SUB-KINGDOM V 



floors of successive layers. Zocecial 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. Zocecial apertures polygonal, 

 rounded, or irregularly 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. Orclo- 

 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, d'Orb. (Fig. 449). 

 Zoaria massive, lobate, or lamellate, 

 encrusting or free. Surface with 

 monticules or plain. Zocccia 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. Zooacia with very thin inflated walls, the apertures irregularly petaloid. 



FIG. 449. 



Monticulipora arborea, Ulr. Trenton ; Minnesota, 

 tical (A) and tangential (B) sections, !*/! (after Ulrich). 



Ver- 



Fio. 450. 



Atactoporella typicalis, Ulr. Black River Group ; Minnesota. Surface (A), tangential (), and vertical (Q 

 sections, 14/x (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 zooscial 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.] 



