172 DEVONIAN FAUNA. 



From the common F.fanata it is distinguished by the regular oval shape and 

 uniformity of its fenestrules, by its much coarser dissepiments, and by other 

 features ; from F. subreticularis, Sandberger, it differs in having larger and less 

 circular fenestrules, less prominent branches, and more numerous cells in each 

 fenestrule. 



4. Fenestella, sp. PI. XX, figs. 3, 3 a. 



Description. — Zoarium small, conical or ovoid, reticulate. Branches exteriorly 

 convex, straight, or slightly undulating, bearing two ranges of large cells, and 

 apparently without a keel. Dissepiments short, straight, nearly as broad as the 

 branches. Fenestrules rather elongate, sub-oval, about one and a half times 

 as long as broad, about twelve in 10 mm. longitudinally, and twenty in 10 mm. 

 horizontally, rather wider than the branches. Cells about four to the length of 

 a fenestrule, with large prominent, lateral, circular mouths opening on the 

 external face. 



Size. — A small but apparently perfect specimen measures 10 mm. long by 

 4 mm. wide. 



Locality. — There is one specimen from Lummaton in the Woodwardian 

 Museum, and another in my Collection. 



Remarks. — The distinctive characteristic of this fossil is that its cell-openings 

 are on the external side. There seems some ambiguity as to the side on which 

 the cell-openings are in the genus Fenestella. Phillips remarks, " the main 

 distinction between this group and Retepora is in the position of the pores or 

 cellules, which are internal in Retepora and external in Fenestella." M'Coy gives 

 the same character. Ulrich, on the other hand, describes the cell-openings as 

 " on the inside (always ?)." Hence there seems a decided difference of opinion on 

 this point, and in particular cases of fragmentary or of flabellate specimens it may 

 be very difficult to decide. In the present species, however, the cell-mouths are 

 certainly on the external face, while in the common F. fanata they seem to be 

 as clearly on the internal surface, and it also differs from that species in having a 

 finer reticulation, stouter dissepiments, and larger cell-mouths. There is, of 

 course, a possibility that an external guard might have existed, though of this 

 there are no signs in the specimen. 



