280 MOLLUSCOIDEA BRYOZOA SUB-KINGDOM v 



compressed, dichotomously dividing, straight-edged branches, attached to foreign bodies 

 by a continuous expanded base. Ordovician and Silurian. 



Eurydictya, Dicranopora, Goniotrypa, Ulrich. Ordovician. 



Euspilopora, Ulrich. Small, irregularly divided branches, with serrated or wavy 

 edges. Devonian. 



Phyllodictya, Ulrich. Zocecial tubes long, with complete diaphragms, but no 

 hemisepta. ' Ordovician. 



Pachydictya, Trigonodictya, Ulrich. Ordovician and Silurian. 



Family 3. Cystodictyonidae. Ulrich. 



Zoaria consisting of two or three layers of cells grown together back to back, forming 

 branching, perforated, or entire leaf-like expansions, or triangular branches. Primitive 

 cells semi-cordate or obovate-acuminate in outline, arranged longitudinally. Primitive 

 aperture sub-circular, but becoming drawn out into a tubular vestibule as growth proceeds. 

 Superficial aperture with peristome, and more or less well-developed lunarium. Interzocecial 

 spaces occupied by vesicular tissue, often filled with a calcareous deposit near the surface. 

 Silurian to Carboniferous. 



Cystodictya, Ulrich. Zoaria ramose, branches sharply elliptical, with sub-parallel, 

 non-poriferous margins. Interapertural spaces finely striated, granulose or smooth ; 

 pits and cells showing only in a worn condition. Silurian to Carboniferous. 



Coscinium, Keyser (Coscinotrypa, Hall) ; Dichotrypa, Ulrich. Silurian to Car- 

 boniferous. 



Taeniopora, Nich. Distinguished from Cystodictya by having a longitudinal ridge 

 or keel, which divides each face into two equal parts. Devonian. 



Prismopora, Scalaripora, Hall. Devonian. 



Evactinopora, Meek and Worth. Zoaria free, consisting of four or more vertical 

 leaves arranged in a stellate or cruciform fashion. Sub-Carboniferous. 



Glyptopora, Ulrich. Zoaria consisting of thin expansions traversed on both surfaces 

 by salient ridges, or of uni-laminate bases on which the coalescing ridges of the upper 

 surface are greatly developed and form large leaves. These ridges or leaves are 

 composed of two layers of cells growing in opposite directions from a mesial lamina. 

 Upper surface with solid maculae or " dimples." Sub-Carboniferous. 



Rhinopora, Hall. Zoaria forming large undulating expansions, the free margins 

 thickened or sharp and non-poriferous. Surface without maculae or monticules, but 

 exhibiting thread-like bifurcating ridges, which appear as shallow grooves when the 

 surface is worn. Large median tubuli between the mesial laminae. Silurian. 



Family 4. Arthrostylidae. Ulrich. 



Zoaria articulated, consisting of numerous sub-cylindrical segments united into small 

 pinnate or bushy colonies, or of continuous, dichotomously divided branches. Zooscia sub- 

 tubular, more or less oblique, radially arranged about a central axis, and opening on all 

 sides of the segments; or one side may be non-celluliferous and longitudinally striated. 

 Ordovician and Silurian. 



Arthrostylus, Ulrich. Zoaria bushy, dichotomously branching, the whole consisting 

 of numerous exceedingly slender, equal, sub-quadrate segments, united by terminal 

 articulation. Zocecia usually arranged in three rows between longitudinal ridges ; the 

 fourth face with longitudinal striae only. Ordovician. 



Helopora, Hall. Like the preceding, but the segments are larger, and have 

 zoo3cial apertures on all sides. Ordovician and Silurian. 



