ORDER IV 



CRYPTOSTOMATA 



341 



Fenestella Lonsd. (Fenestrella d'Orb. ; Actinostoma Youiig) (Fig. 498). Zoaria 

 Üabellate or fimnel-shaped, poriferous on the inner side. Branches connected at 

 regulär intervals by dissepiments. Zooecia in two rows, separated by a piain or 

 tuberculose median keel. Silurian to Permian. 



Semicoscinium Front {Garinopora Nich. ; Cryptopora ^ich.; Gycloporina Simpson). 

 (Fig. 499, e). Zoaria fimnel-shaped, poriferous on the outer side. Dissepiments 

 Wide, very short, the branches appearing to anastomose on the non-poriferous face, 

 vvhere the fenestrules are sub-rhomboidal or rounded. ZocEcia in two ranges, median 

 keel very high and expanded at the summit. Silurian and Devonian. 



Fenestrapora Hall. Like the preceding, except that the reverse of the zoarium 

 and the expanded summits of the carinae bear large, scattered pores, or pits. 

 Devonian. 



(i, Archimedes dlstans Ulr. 

 d, Unitrypa acaulis Hall, ö/ 



(afLer Ulrich, Hall, and Simpson). 



Fig. 499. 



l/l. h, Polypora simulatrix Ulr. i/i and y/j. 

 e, Semicoscinium interruptum H. and S. "/i. 



:, Hemitrypa proutana Ulr. S/j. 

 /, FenestraZia compacta Ulr. ö/j 



Helicopora Claypole ; Isotrypa, Loculipora, Unitrypa Hall (Fig. 499, d). Silurian 

 and Devonian. 



Hemünjpa Phill. (Fig. 499, c). Differs from Fenestella in having a reticulated 

 superstructure, wliose meshes correspond in position and number with the zooecial 

 apertures in the branches beneath. Silurian to Lower Carboniferous. 



Archimedes Lesueur (Fig. 499, a). Distinguished from Helicopora by its solid 

 central axis. As a rule, the fenestrated expansion is broken away, leaving only the 

 screw-like axis. Lower Carboniferous. 



Lyropora Hall. Zoaria flabellate, the fenestrated portion spread between the 

 arms of a non-celluliferous U- or V-shaped support ; free or pedunculate at the base. 

 Zooecia in from two to five rows. Lower Carboniferous. 



Fenestralia (Prout F'ig. 499, /). Having a median keel as in Fenestella^ but with 

 four ranges of zooecia instead of two. Lower Carboniferous (St. Louis Group). 



Polypora M'Coy {Protoretepora Koninck) (Fig. 499, h). Differs from Fenestella 

 in having two to eight rows of cells on a brauch, and in wanting a median keel. 

 The latter is sometimes represented by a row of strong tubercles. Silurian to 

 Permian. 



Thamniscus King. Like Polypora, but branches bifurcating more freely, and with 

 only a few dissepiments or none. Silurian to Permian. 



Phyllopora King. Zoaria funnel-shaped, celluliferous on the outer side, and con- 



