276 



MOLLUSCOIDEA BEYOZOA 



SUB-KINGDOM V 



Family 5. Const ellariidae. Ulrich. 



Zoaria ramose, frondescent, laminar, or encrusting. Zoos^ial 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 zocecia, at intervals gathered into usually stellate clusters; closed at the surface, the 

 closure with numerous perforations. True acanthopores wanting, but small hollow spines 

 or granules often very abundant. Diaphragms straight and complete in both sets of tubes. 

 Ordovician and Silurian. 



Constellaria, Dana (Fig. 461). Zoaria growing erect from a basal expansion which 

 is attached to foreign bodies. Surface with depressed stellate maculae, the spaces 

 between the rays elevated and occupied by two or three short rows or clusters of 



FIG. 461. 



tial, showing aged condition. 



Constellaria florida, Ulr. Cincinnati, O. A, Vertical section. B, Tangentia 

 C, Average tangential section, all 14/1- D, Branch of the natural size (after Ulrich). 



closely approximated zocecial apertures. Mesopores aggregated in the maculae, inter- 

 nally with gradually crowding diaphragms. Ordovician. 



SteUipora, Hall (non Hagw. nee Haime). Differs from the above in its encrusting 

 habit, and in having only mesopores in interspaces between the raised zooscial clusters. 

 Ordovician. 



Nicholsonella, Ulrich (Fig. 462). Laminar expansions, sometimes giving off 

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



Fio. 4(32. 



Nicholsonella pulchra, Ulr. Lower Trenton ; Tennessee. A. Surface. 7/i. B, Vertical section, 

 gential sections at different levels, M/J (after Ulrich). 



C, Tan- 



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

 zorccial tubes ; the spaces become filled up with age by a calcareous deposit, rendering 

 walls of mesopores unrecognisable. Ordovician. 



Idiotrypa, Ulrich ; (?) Dittopora, Dybowski. Silurian. 



