278 



BRITISH GRAPTOLITES. 



Pias. 191 a—c. — Petalograptus palmeus, 

 var. ovato-elongatus, Kurck. 



recognised by its characteristic ovate-elongate shape. When young it is practically 

 impossible to distinguish it from P. palmeus var. latus. 



It varies from 1 — 2*5 cm. in length ; and also 

 within certain limits in the relative extent of the 

 " ovate " and the " elongate " parts. The maximum 

 width of 4—5 mm. is reached practically at once, 

 and may be maintained for a well-marked distance 

 if the ovate part is long. A diminution in width 

 always takes place, sometimes gradually, at others 

 somewhat abruptly, and this decreased width is then 

 maintained to the distal extremity of the polypary ; 

 the part thus diminished in breadth constitutes the 

 elongate portion of the polypary. 



In the ovate part the thecos have a length of 

 2'5 mm., and are about four times as long as wide, 

 but their dimensions are less than this in the elongate 

 part. The thecse are widest at their apertures. In 

 the ovate part they are inclined at 45°, but the 

 angle diminishes to 20° in the elongate part. 



The septum does not seem to be complete till 

 four pairs of thecos have been developed. 

 Horizon and Localities. — Birkhill-Gala. 

 8. Scotland : Dobb's Linn ; Garple Linn, etc. Lake District : Skelgill, Mealy 

 Gill. Wales : Conway. 



Associates, etc. — Var. ovato-elongatus is a fairly abundant fossil in the upper 

 part of the Birkhill Shales. It appears early in the zone of Monog. gregarius, and 

 survives into the Lower Gala. It is commonly associated with the typical form, 

 var. latus, Monog. gregarius, M. convolutus, and Glijptog. tamariscus. 



Collections. — Geological Survey of England and Wales, Sedgwick Museum, 

 Marr, Lapworth, and the Authors. 



a. Obverse aspect, in relief, showing 



sicula. Skelgill, Skelgill Shales. 

 Figured, Elles, Quart. Journ. Geol. 

 Soc, liii, pi. xiv, tig. 12. Coll. Elles. 



b. Young complete specimen (probably 



referable to this variety), showing 

 almost circular form ; reverse as- 

 pect. 



c. Transverse section, showing septum 



and virgula, etc. Skelgill, Skelgill 

 Shales. Figured, Elles, Quart. Journ. 

 Geol. Soc, liii, pi. xiv, fig. 8 (as var. 

 latus). Coll. Elles. 



Petalograptus cfr. ovatus (Barr.). Plate XXXII, fig. 0. 



1850. GraptoJithus ovatus, Barrande, G-rapt. de Boheme, i, p. 63, pi. iii, figs. 8, 9. 



1851. Petalolithus ovatus, Suess, Ueber Bohmische Graptolithen, p. 21, pi. viii, fig. 3. 



1852. Diplograpsus ovatus, Geinitz, Die Graptolithen, p. 20, pi. i, figs. 3 and 4. 



1890. Dipdngraptus ovatus, Geiuitz, Graptolithen des lc. mineralog. Mus. Dresden, p. 25, pi. a, 



fig. 37. 

 1897. Petalograptus ovatus, Elles, Quart. Journ. Geol. Soc, vol. liii, p. 199, pi. xiv, figs. 15, 16. 



Polypary very small, ovate, nearly as wide as long. Sicula large. Thecse at 

 rate of twenty-eight in 10 mm., very long and narrow, with slight curva- 



