334 



MOLLUSCOIDEA— BRYOZOA 



PHYLUM V 



Atadopora Ulr. (Fig. 483). Zoaria thin, growing on Ortlwceras. Zocecial apertures 

 indented or floriform, according to jjosition of the very numerous acanthopores. Eather 

 large, solid elevations, composed of abortive cells, and completely filled by calcareous 

 deposit, stud the surface at regular intervals. Ordovician and Silurian. 



Leptotrypa Ulr. Ordovician. Gyphotrypa U. and B. Ordovician to Devonian. 



Family 3. Oonstellariidae Ulrich. 



Zoaria ramose, frondescent, laminar or encrusting. Zooscial tubes thin-walled and 

 prismatic in the axial region, thicker and sub-cylindrical in the peripheral; apertures 

 rounded, the peristomes slightly elevated. Mesopores angular, abundant, generally 

 isolating the zooecia, at intervals gathered into usually stellate clusters; closed at the 

 surface, the closure tvith numerous perforations. True acanthopores loanting, but small 

 hollow spines or granules often very abundant. Diaphragms straight and complete in 

 both sets of tubes. Ordovician and Silurian. 



Constellaria Dana (Fig. 484). Zoaria growing erect from 



attached basal 

 D 







w&^ 





?S!I 





Pifi. 4S4. 



Constellaria florida \Jlr. Cincinnati, Ohio. J, Vertical section. i>', Tangential, sliowing aged condition. 

 C, Average tangential section, all i4/j. D, Branch of the natural size (after Ulrich). 



expansion. Surface with depressed stellate maculae, the spaces between the rays 

 elevated and occuijied by two or three short rows or clusters of closely approximated 

 zocecial apertures. Mesopores aggregated in the maculae, internally with gradually 

 crowding diaphragms. Ordovician. 



Stellipora Hall {non Hagw. nee Haime). Differs from the above in its encrusting 

 or lamellate habit, and in having only mesopores in intersjiaces between the raised 

 zocecial clusters. Ordovician. 



Nicholsonella Ulr. (Fig. 485, A-G). Laminar expansions, sometimes giving off' 



^^f* 





Flc. 485. 



NieJiolsoiieUii pnlchra Ulr. Stones River; Tennessee. A, fSiirface, 7/j. £, Vertical section, w/v C, Tan- 

 gential sections at diflerent levels, K/j (after Ulrich)- 1^, JJianulites fastigiatus Bichw. Silurian ; Baltic 

 Provinces. Tangential section, I'l/j (after Bassler). 



flattened, intertwining branches or fronds. Interzooecial spaces wide, and with 

 numerous mesopores, whicli have thicker and more numerous diaphragms than tl.ie 



