I^y ORDER III 



TREPOSTOMATA 



331 



and floors of successive layers. Zooecial Covers with a small, usually sub-central orifice. 

 Monticules or maculae (containing cells differing from the average in size, or in hxiving 

 their apertures elevoAed) regiilarly distributed over the snrface. 



The Trepostomata include the greater j^ortion of the " Monticuliporoids " which 

 by some writers, particularly Milne Edwards and Haime, were regarded as Anthozoans. 

 Nicholson assigned them to the Octocoralla becaiise the corallites apparently agreed 

 with Heliolites in their microscopic structure, and in addition were snpposed to have 

 iniperforate walls and to increase by intermural gemmation or by fission. Ulrich 

 has insisted upon the bryozoan natiire of these organisms, and has published niany 

 facts militating against Nicholson's views. Bassler has added a number of points 

 confirmatory of their bryozoan affinities, and recently Cumings has worked out the 

 primitive budding stages of at least six characteristic genera. He finds that the 

 budding plan of Prasopora and allied genera is precisely the same as in typical recent 

 Bryozoa, namely that it consists of (1) a protoecium, or minute circular disk ; (2) the 

 ancestrula^ a tubulär zooGcium of the type seen in the Cyclostomata ; and (3) several 

 primary buds arising from and adjacent to the ancestrula. These primitive structures 

 are separated from the rest of the colony by a considerable thickening of their 

 posterior walls. In the Corals, development from the planula is direct, the moment 

 it becomes sedentary and therefore the presence of the protcecium alone is practically 

 conclusive as to the systematic position of the Trepostomata with the Bryozoa. 



Suborder A. AMALGAMATA Ulrich and Bassler. 



Trepostomata in which the houndaries of adjacent zooecia are ohscured by the more or 

 less complete amalgamation of their walls. 



Family 1. Monticuliporidae Nicholson (emend, Ulrich). 



Zoaria multiform. Zooecial apertures polygonal, rounded or irregularly petaloid. 

 Mesopores occasionally wanting, in other cases numerous, angular and crossed by 

 crowded diaphragms. Acanthopores A B 



always present in the mature region. 

 Ordovician to Devonian. 



The incomplete, curved, transverse 

 partitions, termed cystiphragms by 

 Ulrich, are the principal peculiarity of 

 this family. It is possible that tliey 

 represent ovicells, but their significance 

 can only be conjeetured. 



Monticulipora d'Orb. (Fig. 474). 

 Zoaria incrusting to massive. Zooecia 



Fig. 474. 



T 1 -^1 • ^ 1 1 MoniicuXipwaarhoreamT. Trenton ; Minnesota. Vertical 



polygonal, with mmutely granulöse ^^^ ^n^ tangential (ß) sections, i-«/i (after Ulrich). 



walls. Cystiphragms lining both 



mature and immature regions. Mesopores very few or absent. Acanthopores small, 



granulöse, more or less numerous. Ordovician and Silurian. 



Orbignyella U. and B. Ordovician to Devonian. 



Ätactoporella Ulr. (Fig. 475). Zoaria generally encrusting. Zooecia with veiy 



pores, were doubtless occupied by specially niodified polypides, which probably find tlieir 

 homologues in the avicularia and vibracula of recent Chilostomata. But niany of the mesopores 

 wliich are not invested by separate walls are to be regarded as mere iuterspaces between the 

 zooecial tubes, and the purpose of their transverse partitions is to support the walls of the latter, as 

 well as to assist intercomniunication by nieans of the zoarial parenchynial cord. 



