SUB-ORDER c CRYPTOSTOM AT A 279 



r/n'/nstamata, which have the same tubular prolongation of tlie aperture. Thus, the recent 

 A'i> on- f/it "//"/'//<", Busk, has not only a vestibule, but hemisepta as well. Hemisepta are 

 nevei found in tin- <';/</< istmiuita and Trepostomata, but are a very common feature of the 

 rritfifiixti'iH'if't. They occur at the bottom of the vestibule, and doubtless served as supports 

 for the movable operculum. 



Family 1. Ptilodictyonidae. Ulrich. 



Zoaria bifoliate, composed of two layers of zocecia grown together back to back, con- 

 tinuous or joint' <l, n,,,] fumiinii lif-like expansions, or compressed, branching, or inosculating 

 stems. Mesial plates 'without median tubuli ; hemisepta usually present. Inner orifice 

 i> // mil if * nii-i/lijitii-nl, the outer more rounded, usually ovate, and surrounded by either a 

 .<loj>in<l area or a ring-like peristome. Vestibules separated by thick walls. Ordovician to 

 Sub-Carboniferous. 



Ptilodictya, Lonsd. (Heterodictya, Nich.) Zoaria simple, unbranched, lanceolate, 

 or falciform, with a small basal expansion. In the young condition the zoarium 

 consists of longitudinally arranged, narrow, oblong-quadrate zoo3cia, new zooecia, of 

 different width and arrangement, being added subsequently on each side. In the 

 vestibular or outer region the walls are more or less thickened, solid, and with a 

 double row of exceedingly minute dots. Ordovician to Devonian. 



Escharopora, Hall (Nicholsonia, Waag. and Wentz). Distinguished from the last 

 chiefly by the arrangement of the zocecial apertures, which are in diagonally inter- 

 secting series, and by the hexagonal sloping area which surrounds the external orifice. 

 Ordovician. 



Clathropora, Hall. Zoaria composed of anastomosing branches forming a regular 

 network with round fenestrules, terminating below in a pointed, articulating base. 

 Zooecial apertures usually sub - quadrate, arranged longitudinally. Ordovician to 

 Devonian. 



Phaenopora, Hall. Zoaria as in Ptilodictya, except that there are two mesopores 

 in each interspace between the ends of the zoo2cial apertures. Ordovician and 

 Silurian. 



Arthropora, Ulrich. Zoaria bushy, spreading in a plane, composed of numerous 

 equal segments. Zooecial apertures elliptical, surrounded by a delicate peristome. 

 Interspaces with one or more threadlike ridges, variously disposed, and with a row 

 of minute papillae. Ordovician. 



Graptodictya, Ptilotrypa, Ulrich ; Ordovician. Taeniodictya, Ulrich ; Devonian 

 and Sub-Carboniferous. 



Stictotrypa, Ulrich. Brandies not jointed at the base. Zooecial apertures 

 circular or elliptical, with a distinct, evenly elevated peristome. Ordovician and 

 Silurian. 



Stictoporella, Ulrich. Zoaria variously formed, with elliptical apertures placed at 

 the bottom of a sloping area. Thick-walled, untabulated mesopores occur between 

 the zocecial apertures and line the zoarial margins. Ordovician to Sub-Carboniferous. 



Intrapora, Coscinella, Hall. Devonian. 



Family 2. Bhinidictyonidae. Ulrich. 



Zoaria bifoliate, continuous or jointed, forming compressed branches or leaf-like expan- 

 sions ; occasionally trifoliate. Primitive cells sub-quadrate, arranged longitudinally. Both 

 primitive and superficial apertures elliptical or sub-circular, sometimes a little truncated 

 posteriorly. Inferior hemiseptum and lunarium wanting. Median tubuli present between 

 the median laminae, and between the longitudinal rows of zocecial tubes. Mesopores absent, 

 but vesicular tissue often present. Chiefly Ordovician. 



Rhinidictya, Ulrich (Stictopora, Ulrich 11011 Hall). Zoaria composed of narrow, 



