FENESTELLA. 185 



I. Family FEXESTELLID.E, King, 1849. 

 1. Genus FENESTELLA, Lonsdale, 1839. 



1. FEXESTELLA PLEBEIA, WCoy. Plate XXII, figs. 14 15 a; and Plate XXIII, 



figs. 1, 1 a. 



1841. FEXESTELLA ANTIQUA? vars. /3 ? and y, Phillips. Pal. Fos?., p. 24, pi. xii, 



fig*. $5 (rf, /)/,* 



1844. PLEBEIA, M'Coy. Synops. Carb. Foss. Irel., p. 203, pi. xxix, 



fig. 3. 



1855. Brit. Pal. Foss., p. 76. 



1879. Shrubsole. Quart. Jourri. Geol. Soc., vol. xxxv, 



p. 278. 

 1881. Ibid., vol. xxxvii, p. 179. 



Description. Zoarium apparently flabelliform, large. Fenestrules about nine 

 or ten in the length of 10 mm., and thirteen in the width of 10 mm., elongate, 

 oblong. Branches stout, undulating near the base, almost straight in the distal 

 parts, about the width of the fenestrules, and divaricating at first irregularly and 

 farther from the base at very regular distances. Dissepiments apparently small 

 and narrow. Non-poriferous surface ornamented with a few strong longitudinal 

 ridges. Mode of increase sometimes near the base by one or two new branches 

 rising from the closed head of a fenestrule, but generally by the simple fission of 

 the branches, which appears to occur at the rate of once in about ten fenestrules, 

 and at the same level in groups of adjoining fenestrules. Cells arranged in two 

 alternating rows, sometimes with a third cell intercalated at the commencement 

 of a branch, pentagonal in longitudinal section, numbering from four to six, 

 generally five, in the length of a feuestrule. 



Size. A fragmentary specimen is 50 mm. long. 



Localities. Poleshill, Wrafton Lane, Pilton, Ashford Strand, Snapper 

 Quarry, Kingscote (near Brushford), Croyde, &c. It is an abundant species, 

 and is found at most of the Pilton localities, though it is not so frequent in beds 

 where large Brachiopods predominate. 



Remarks. This appears to be the species described by Phillips from North 

 Devon under the name " Fenestella antiqua, (?), Lonsdale, var. /3 and y" though 

 under these varieties he also included the South Devon form, which I have called 

 F. fanata, 1 and from which it differs in its less rapid branching, the larger number 

 of cells to a fenestrule, and other points. M'Coy, in 1855, separated the form 

 found at Petherwyn from the Middle Devonian species, and referred it to his pre- 



1 1895, \Yhidborne, ' Dev. Fauna,' vol. ii, p. 165, pi. xviii, figs. 610 ; and pi. xix, figs. 3, 4. 



