282 



MOLLUSCOIDEA BKYOZOA 



SUB-KINGDOM V 



Fenestropora, 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. 



Isotrypa, Loculipora, Unitrypa, Hall. Silurian and Devonian. 



Hemitrypa, Phill. Differs from Fenestella in having a reticulated superstructure, 

 whose meshes correspond in position and number with the zocecial apertures in the 



FIG. 467. 



Fenestella retiformis, Schloth. Permian Dolomite ; Possneck, Thuringia. A, Fragment of zoarium, natural 

 size. B, Portion of external surface, slightly enlarged. C, Magnified portion of interior celluliferous surface. 



branches beneath. The structure rests on pillars which rise at regular intervals from 

 the moderate median keel of the branches. Silurian and Devonian. x 



Helicopora, Claypole. Zoaria spiral, the inner edge thickened and non-poriferous, 

 but not forming a solid axis. Otherwise like Fenestella. Silurian, (?) Devonian. 



Archimedes, Lesueur (Fig. 468). Distinguished from Helicopora by its solid central 



FIG. 468. 



Archimedes Wortheni, Hall sp. Sub-Carboniferous; Warsaw, 111. A, Fragment of well-preserved zoarium, 

 Vi (after Roemer). B, Broken spiral zoarium (after Quenstedt). C, Portion of interior or upper surface of the 

 expansion, enlarged (after Roemer). D, External or inferior aspect of same (after Hall). 



axis. As a rule, the fenestrated expansion is broken away, leaving only the screw-like 

 axis. Sub- 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. 

 Zocecia in from two to five rows. Sub-Carboniferous. 



Fenestralia, Prout. Having a median keel as in Fenestella, but with four ranges of 

 zocecia instead of two. Sub-Carboniferous (St. Louis Group). 



Polypora, M'Coy. Differs from Fenestella in having two to eight rows of cells on a 

 branch, and in wanting a median keel. The latter is sometimes represented by a row 

 of strong tubercles. Silurian to Carboniferous. 



