SUB-ORDER c CRYPTOSTOMATA 28 1 



Sceptropora, Ulricli. Segments short, greatly expanded above, celluliferous all 

 around. Ordovician and Silurian. 



Arthroclema, Bill. Segments sub-cylindrical, celluliferous on all sides, arranged 

 pinnately. Articulation both terminal and lateral. Ordovician. 



Nematopora, Ulrich. Xi.ari.-i very slender, ramose, continuous above the pointed 

 basal extremity. Zocecia sub-tubular, arranged radially about one or two minute axial 

 tubes. Ordovician and Silurian. 



Family f>. Rhabdomesodontidae. Vine. 



Zoaria ramose or simple, not articulated, sometimes with a large or small axial tube, 

 and generally solid. In the latter case the axial region is occupied by thin-walled primitive 

 tubes, with or without diaphragms. Hemisepta usually present, but never conspicuous. 

 External zocecial apertures oval or circular, regularly arranged, and usually at the bottom 

 of a rhombic or hexagonal sloping area, or between longitudinal ridges. Mesopores absent. 

 Silurian to Carboniferous. 



Rhombopora, Meek (Orthopora, Hall). Zoaria slender, ramose, solid. Zocecial tubes 

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

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

 to Carboniferous. 



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

 pointed. Sub-Carboniferous. 



Ehabdomeson, Young. Differs from Bhombopora only in having a slender axial 

 tube, to which the proximal ends of the zooecia are attached. Carboniferous. 



Goeloconus, Ulrich. Zoaria simple, hollow, expanding gradually from the striated 

 base ; substance thin. Primitive portion of zocecia short, with well-developed hemi- 

 septa. Sub-Carboniferous. 



? Tropidopora, Hall ; Devonian. (?) Streblotnjpa, Ulrich ; Devonian and Sub- 

 Carboniferous. 



Family 6. Fenestellidae. King. 



Zoaria forming reticulate expansions, celluliferous on one side only. They are composed 

 of rigid branches united by regular non-poriferous bars (dissepiments] or may be sinuous 

 and anastomose at regular intervals ; or may remain free. Zooecia enclosed in a calcareous 

 crust, ivhich is minutely porous, especially on the non-celluliferous side. Primitive portion 

 of zooecia oblong, quadrate, or hexagonal in outline. Superior hemiseptum usually present, 

 the inferior one less frequently. Primary orifice anterior, semi-elliptical, truncated behind. 

 External apertures rounded, with peristome, and covered, when perfect, by centrally perforated 

 closures. Ordovician to Permian. 



The zoarial characters of the Fenestellidae are extremely constant, and are of the greatest 

 systematic importance. The xocecial cavity in this family is very similar to that of the Ptilo- 

 dictyonidae and Ehinidictyonidae ; and the same is also true of both the primary and external 

 orifices. Ulrich considers the family as having been derived from Phylloporina. 



Fenestella, Lonsd. (Fenestrella, d'Orb. ; Actinostoma, Young), (Fig. 467). Zoaria 

 flabellate or funnel-shaped, poriferous on the inner side. Branches generally straight, 

 sometimes flexuous, connected at regular intervals by dissepiments. Zorccia in two 

 rows, separated by a plain or tuberculose median keel. Ordovician to Permian ; 

 chiefly Devonian and Sub- Carboniferous. 



Semicosminium, Prout ^Carinopora, Nich.) Zoaria funnel-shaped, poriferous on 

 the outer side. Dissepiments wide, very short, the branches appearing to anastomose 

 on the non-poriferous face, where the fenestrules are sub-rhomboid al or rounded. 

 Zocecia in two ranges, median keel very high and expanded at the summit. Silurian 

 and Devonian. 



