ORDER IV 



CRYPTOSTOMATA 



343 



Sce'ptro'pora Ulr. Segments short, greatly exi^anded above, celluliferous all around. 

 Ordovician and Silurian. 



f 



fA^^-'' 





V>V 



Fi(i. 5(11. 



a, Arthrodema hlUimjsi Ulr. %. 6, --1. nrmatum Ulr. Sef;ment, i2/j. e, Nematopora muferln. Ulr. 

 d, e, Arthrostijhis conjunctus Ulr. i2/i. /, Hchporu harrisi Ulr. l^/j (after Ulricli). 



'Vi 



Arthrodema Bill. (Fig. 501, a, b). Segments sub-cylindrical, cellidiferous on all 

 sides, arranged pinnately. Articulation both terminal and lateral. Ordovician. 



Nematopora Ulr. (Fig. 501, c). Zoaria very slender, 

 ramose, continuous above the pointed basal extremity. Zooecia 

 sub-tubular, arranged radially about one or two minute axial 

 tubes. Ordovician and Silurian. 



Glauconome Goldf. {Penniretepora d'Orb.). Zoarium branch- 

 ing continuously ; reverse side non-celluliferous ; zooecia as in 

 Nematopora. Ordovician and Silurian. 



Family 5. Rhabdomesontidae Vine. 



Pig. 502. 



Zoaria ramose or simple, not articulated, sometimes tvith a 

 large or small axial titbe, and generally solid. In the latter 



case the axial region is occupied by thin-walled primitive tubes, Helopom spini/ormis uir. 

 vjith or loithout diaphragms. Hemisepta usually present, but ^i°"verticai'^^section°*'*'i'-vt.' 

 never conspicuotis. External zocccial apertures oval or circular, b, Segment, Vi and i-t/i 

 regularly arranged, and usualhj at the bottom of a rhombic or 



hexagonal sloping area, or between longitudinal ridges. Mesopores absent. Ordovician 

 to Permian. 



Bhomhopora Meek (Fig. 503, b). Zoaria slender, ramose, solid. Zooecial tul)es 

 with the outer or vestibular region thick-walled, apertures arranged in diagonal 

 or longitudinal lines. Strong acanthopores and smaller spines generally present. 

 Ordovician to Permian. 



Bactropora Hall. Zoaria simple or only slightly branched, the lower extremity 

 pointed. Lower Carboniferous. 



Rhabdomeson Young. Differs from Rhombopora only in having a slender axial' 

 tube, to which the proximal ends of the zooecia are attached. Coal Measures and 

 Permian. 



Goeloconus Ulr. (Fig. 503, a). Zoaria simple, hollow, expanding gradually from 

 the striated base; substance thin. Primitive portion of zooecia short, with well- 

 developed hemisepta. Lower Carboniferous. 



