. The Quarterly journal of the Geological Society of London. set. The pinna? arelanceolate in shape, with entire margins tapering gradually to anacuminate apex. Their bases are rounded, and they are attachedto the rachis by the central portion of the base, which is slightlyconcave in form at the point of insertion. The pinnae are traversedby a number of fine parallel veins. One of the specimens is part of a larger frond, with pinnae8 to 9 cm. long and attaining a width of about 13 mm.; the othermore complete example has much smaller pinnae, only 2 cm. longand 5 mm. wide. The characters of both
. The Quarterly journal of the Geological Society of London. set. The pinna? arelanceolate in shape, with entire margins tapering gradually to anacuminate apex. Their bases are rounded, and they are attachedto the rachis by the central portion of the base, which is slightlyconcave in form at the point of insertion. The pinnae are traversedby a number of fine parallel veins. One of the specimens is part of a larger frond, with pinnae8 to 9 cm. long and attaining a width of about 13 mm.; the othermore complete example has much smaller pinnae, only 2 cm. longand 5 mm. wide. The characters of both specimens are, however,identical: most probably both belonged to the same species, whichoccurs frequently at Whitby, Gristhorpe, and other localities inYorkshire. Another large and typical example is in the collection made bythe late Mr. Hawell, preserved in the Middlesbrough Museum. Thelarge form also occurs at Eoseberry Topping. Pig. 3.—Outlines of portions of two types of fronds referable to the-aggregate species Ptilophyllum (Willianisonia) [A is magnified 2 diameters ; B is of the natural size.]Ptilophyllum (Williamsonia) pecten (Phillips). [ Illustv. Geol. Yorks. pt. 1—The Yorkshire Coast 1829, p. 148 & pi. vii,fig. In most of the Yorkshire fossil-plant localities series of frondsare found which show a considerable range of variation amongthemselves, but are all referable to the type of Pt. pecten. The Yol. 69.] THE CLEVELAND DISTRICT OF YORKSHIRE. 235 collections here described contain a similar large series of frondswhich are, for the present, all included under this species. Severalwell-marked varieties occur; but, as at Whitby,1 they seem to beconnected one with the other by intermediate forms. It is probablethat future work on the structure of the cuticles of these forms 2will show that the principal varieties may be regarded as distinctspecies. I hope to undertake the detailed investigation of thisquestion, when further specimens have been obtaine
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Keywords: ., bookcentury1800, bookdecade1840, booksubjectgeology, bookyear1845
