46 



ON THE GENUS FENESTELLA. 

 By the Eev. J. E. Tenison Woods, F.G.S., &c. 



[Bead Sth June, 1875.] 



As species of Fenestella are very common as fossils in the 

 Devonian rocks, but especially those of Tasmania, a few- 

 observations on the genus and its affinities will be found 

 useful to geologists, 



Fenestella is a genus placed now by all palaeontologists in 

 the Class Polyzoa, Order I, InfuncUhidata. 



Sub order Cheilostoniata, that is to say, with the aperture of 

 the cell filled with a thin membranaceous or calcarious velum, 

 with a crescentic mouth provided with a movable lip. This 

 latter feature in the case of Fenestella is concluded from 

 analogy and certain anatomical details, because the fossils 

 themselves are never so perfectly preserved as to manifest 

 them. 



Fenestella is also placed in the subdivision S. inarticulata 

 or continuous, and in the section himultiserialaria, that is, 

 the cells disposed in a double or multiple series. It is also 

 placed by most authors in the family Escharidce, of which the 

 definition is as follows : — Polyzoarium erect, rigid, foliaceous, 

 and expanded, lobate, or reticulated. Cell disposed quincun- 

 cially in the same plane on one or both sides of the polyzoarium. 

 But in some cases this hardly applies, as the cells are some- 

 times, as in the case of F. internata, Lonsd. in a double series 

 only. The genus was also placed with the Retepora, of which 

 the definition is foliaceous, calcareous, reticulated, cells im- 

 mersed opening on one surface only. But in 1830 Mr. Miller 

 suggested a new genus for certain reticulated polyzoa in the 

 carboniferous limestone which Mr. Lonsdale adopted. All 

 cup-shaped reticulated polyzoa were hitherto called Eetepora, 

 but now it was agreed to name Eetepora those only on which the 

 openings of the cells were inside the cup, and those in which 

 the cells opened on the outside only were henceforth erected 

 into a new genus, and called Fenestella. But difficulties in 

 applying his distinction soon arose. The cup-shaped or 

 conical figure is nearly always absent. In Tasmania the 

 distinction would be of no avail. The polyzoary, though very 

 wavy and irregular, is always fragmentary, and often lies per- 

 fectly flat. Prof. Phillips suggests (Pal. Foss. of Cornwall, 

 Devon, &c., p. 22) another mark of distinction. He says that 

 the non-poriferous surface of Fenestella is usually marked by 

 longitudinal, more or less continuous ribs, united by bars of 

 smaller diameter, leaving oval or subquadrangular spaces. 

 In Eetepora these spaces look more like holes or perforations 



