ORDER III 



TREPOSTOMATA 



331 



and floors of successive layers. Zocecial covers loith a small, usually sub-central orifice. 

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

 their apertures elevaAed) regularly distributed over the surface. 



The Treijostomata include the greater portion of the " Monticuliporoids " which 

 by some writers, particularly ]\Iilne Edwards and Haime, were regarded as Anthozoans. 

 Nicholson assigned them to the Octocoralla because the corallites apparently agreed 

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

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

 has insisted upon the bryozoan nature of these organisms, and has published many 

 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 2Jlan of Prasopora and allied genera is jJi'ecisely the same as in typical recent 

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

 ancestrula, a tubular zocecium of the type seen in the Cyclostomata ; and (3) several 

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

 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 protoecium alone is practically 

 conclusive as to the systematic position of the Trejiostomata A\ith the Bryozoa. 



Suborder A. AMALGAMATA Ulrich and Bassler. 



Trepostomata in which the boundaries of adjacent zocecia are obscured by the more or 

 less complete amalgamation of their walls. 



Family 1. Monticuliporidae Nicholson (emend. Ulrich). 



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

 Mesopores occasionally wanting, in other cases numerous, angula,r and crossed by 

 crowded diaphragms. Acanthopores a /; 



abundant, iisually small. Gystiphragms 

 always present in the mature region. 

 Ordovician to Devonian. 



The incomplete, curved, transverse 

 partitions, termed cystiphragms by 

 Uh'ich, are the principal peculiarity of 

 this I'amily. It is possible that they 

 represent ovicells, but their significance 

 can only be conjectured. 



Monticulipora d'Orb. (Fig. 474). 

 Zoaria incrusting to massiA^e. Zocecia 



Monticulipora arborea Ulr. Trenton ; Minnesota. Vertical 

 (A) and tangential (75) sections, i-i/i (after Ulrich). 



polygonal, with minutely granulose 



walls. Cystiphragms lining both 



mature and immature regions. Mesopores very few or absent. 



granulose, more or less numerous. Ordovician and Silurian. 



Orbignyella U. and B. Ordovician to Devonian. 



Atactoporella Ulr. (Fig. 475). Zoaria generally encrusting, 



Acanthopores small, 



Zocecia with very 



pores, were doubtless occupied by specially modified polypides, which probably find their 

 homologues in the aviciilaria 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 

 zooecial 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 parcnehynial cord. 



