334 



MOLLUSCOIDEA— BRYOZOA 



PHYLÜM V 



Ätactopora Ulr. (Fig. 483). Zoaria thiii, growing on Orthoceras. Zococial apertures 

 iiideiited or floriform, accordiiig to position of the veiy niimerous acanthopores. Ratber 

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

 deposit, stud tbe surface at regulär iiitervals. Ordovician and Silurian. 



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



Family 3. Oonstellariidae Ulrich. 



Zoaria rawose, frondescent, laminar or encrusting. Zooecial tuhes thin-walled and 

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

 rounded, the peristomes slightly elevated. Meso'pores angular, ahundant, generally 

 isolating the ^ocecia, at intervals gathered into usually stellate Clusters ; closed at the 

 surface, the closure with numerous perforations. True acanthopores wanting, hut small 

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

 both sets of tuhes. Ordovician and Silurian. 



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



basal 



Fig. 484. 



Gonstellaria florida Vir. Cincinnati, Ohio. J, Vertical section. i>, Tangential, showing aged condition. 

 C, Average tangential section, all 14/^, j)^ Branch of the natural size (after Ulrich). 



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

 elevated and occupied by two or three short rows or Clusters of closely approximated 

 zooecial 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 interspaces between the raised 

 zooecial Clusters. Ordovician. 



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



Fio. 485. 

 Nicholsonella pulchra Ulr. Stones River; Tennessee. A, Surface, 7/j. ß, Vertical section, i4/^. C, Tan- 

 gential sections at different levels, K/i (after Ulrich). D, Dianulites fastigiatus Bichw. Silurian ; Baltic 

 Provinces. Tangential section, 14/^ (after Bassler). 



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

 numerous mesopores, which have thicker and more numerous diaphragms than the 



