206 



BRITISH GRAPTOLITES. 



Figs. 138 a and b. — Climacograptus sty- 

 loideus, Lapw. MS. 



basal thecse may give off spines from their free 

 outer walls, these are but rarely seen. The virgula 

 is sometimes expanded into a small disc towards its 

 apical extremity; but at varying lengths from the 

 distal end of the polypary. The width of the speci- 

 mens varies with the mode of presentation ; as a 

 rule 2 — 2*5 mm. is the maximum in those which 

 show only a scalariform view, but in those presented 

 in true profile 3 mm. may be measured, though this 

 greater width may be partly due to compression. 

 The excavations, which appear as narrow elliptical 

 slits, are very conspicuous in all states of preserva- 

 tion, and are invariably slightly oblique and inclined 

 downward and inward. 



Affinities. — CI. styloideus is characterised by its 

 relatively small breadth in comparison with its 

 length and by the form of the proximal end. It 

 presents a certain resemblance in size and form to 

 CI. Scharenbergi, but may be readily separated from 

 well-preserved specimens of that graptolite by the 

 absence of the zig-zag septal groove. 



Horizon and Localities. — Hartfell Shales (zone of 

 Pleurog. linearis). 



8. Scotland : Dobb's Linn ; Hartfell ; Glenkiln ; 

 Craigmichan Scaurs. 

 Associates, etc. — CI. styloideus is confined to the Hartfell Shales ; it is a rare 

 fossil in the zone of Pleurog. linearis, and occurs associated with the zone fossil. 

 Collection. — Lap worth. 



a b 



a. Proximal end, showing virgella. En- 



largement of part of specimen on 

 same slab as PI. XXVII, fig. 9 c. 



b. Proximal end, showing various as- 



pects of the thecoe. Enlargement 

 of part of specimen on same slab as 

 PI. XXVII, fig. 9 a. 



Fia. 138 c — Climacograptus styloideus, 

 Lapw. MS. 



P 



% 



c. Distal thecae. Enlargement of part 

 of PL XXVII, fig. 9d. 



Group TIL 



Climacograjpti in which the free edge of the theca is practically straight and 

 vertical, and the apertural margin slightly introverted and introtorted. 



Climacograptus Scharenbergi, Lapworth. Plate XXVII, figs. 14 a- 



1851. Prionotus, Boeck, Bemaerkniiiger angaacnde Graptolitherne, pi. i, figs. 3, 10, 15, 18. 

 1851. Graptolithus (Diplograpsus) teretiusculus, Scharenbcrg, Ueber Graptoliten, pi. ii, figs. 23 a, 

 24 a, 25 a, 31 a. 



