PINNA FLABELLIFORMIS. 3 



of sinuosity or interruption. These ridges are crossed by obscure lines of growth, 

 which are concentric with the posterior border. 



Dimeiisioii.s. — Specimens may grow to an immense size. De Koninck figures a 

 specimen which measures — 



Antero-posteriorly .... 350 mm. 

 Dorso-ventrally . . . .120 mm. 



Thickness . . . . .40 mm. 



LocaUUes.— England : the Carboniferous Limestone of Narrowdale, Stafford- 

 shire ; Castleton, Derbyshire ; Cracoe and Thorpe, Yorkshire ; Poolvash, Isle of 

 Man. Shale above Great Scar and Middle Limestones, Wensleydale. Shale above 

 Underset Limestone, Swaledale; Lowick, and Ironstone series of Redesdale, 

 Northumberland. Scotland: the Upper Limestone series of Newfield, Arden, 

 Bishopriggs ; the Lower Limestone series of Beith and Hind og Glen ; the 

 McDonald Limestone, Muirkirk, Lugton Water, Waterland ; Burn Anne; the 

 Lower Limestone series of Fife ; north of Laggan, Arran, twenty feet above the 

 Hurlet Limestone; Upper Limestone series, Corrieshore ; Maol-Doun, in shale 

 below the Hurlet, Bute ; Scolieburn, Edinburgh. Ireland : Carnteel and Benburb, 

 CO. Tyrone ; Bunnowa, Easky, co. Sligo. 



Obsemntioii^. — Following de Koninck, I consider that the four species 1'. 

 flahelliformis, Martin, P. codnta, Phillips, P. inaBqiucostata and i'. liexlcostata , 

 M'Coy, are one and the same species ; the differences considered by these authors 

 to be of specific value being mere irregularities in the surface ornament, often due 

 to growth. P. ffrxicostata, M'Coy, is founded on a series of internal casts from 

 Lowick, PI. II, figs. 1, 0. These specimens are in the Woodwardian Museum, 

 Cambridge, and are casts of the right and left valves. 



PI. II, fig. 2, is the type of M'Coy's P. iiisRquicoHfafa [op. supra fit.), and consists 

 of a section from the middle of the valve, also a cast. The specimen is in the Griffitli 

 Collection of the Museum of Science and Art, Dublin, and I am grateful to the 

 authorities for permission to refigure the various types. 



I have only been able to figure small and incomplete examples. The shell 

 grows to a considerable size, as is shown by the very fine specimen figiired l)y de 

 Koninck {op. supra rit., pi. xxvii, figs. 1 and 2). The author points out that the 

 apical angle of all the various shells now referred to P. flaheUiforinis is practically 

 identical, and that in consequence of the youth and preservation of the specimens, 

 modifications of the ornament, due to age, have not been appreciated by previous 

 observers; but even de Koninck did not recognise the fact that all the figured 

 examples of P. fiexicostata were casts of the interior. 



The type of P. insequicostata, Portlock, is refigured PI. IV, fig. 1. 



