SUB-ORDER C CRYPTOSTOMATA 281 
Sceptropora, Ulrich. 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. Zoaria 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 5. 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 zowcial 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. 
Rhabdomeson, Young. Differs from Rhombopora only in having a slender axial 
tube, to which the proximal ends of the zocecia are attached. Carboniferous. 
Coeloconus, 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. (?) Streblotrypa, 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. Zoecia enclosed in a caleareous 
crust, which is minutely porous, especially on the non-celluliferous side, Primitive portion 
of zowcia 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 Fenestel/idae are extremely constant, and are of the greatest 
systematic importance. The zocecial cavity in this family is very similar to that of the Ptilo- 
dictyonidae and Rhinidictyonidae ; 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. Zoacia 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-rhomboidal or rounded. 
Zocecia in two ranges, median keel very high and expanded at the summit. Silurian 
and Devonian. 
