

DIPLOGRAPTUS. 225 



Var. spinigerus, Lapworth. Plate XXVIII, figs. 2 a—d. 



1876. Diplograptus guadrimucronatus var. spinigerus, Lapworth, Cat. West. Scott. Foss., pi. ii, fig. 43. 



In addition to the typical form already described, there occurs a second form 



of Orthog. quadrimucronatus, which appears to be sufficiently distinct to be classed 



,,. _ J7 , , . as a variety. It occurs on the same horizon as 



Fin. 146. — Orthograptus quadnmucro- J 



natus, var. spinigerus, Lapw. () quadrimucronatus, but is usually larger, and has 



abnormally developed spines on the thecse about 

 8 mm. from the proximal end, this position corres- 

 ponding apparently with the tenth thecal pair. 

 These thecse are each furnished typically with a 

 pair of long curved spines having a length of 5 mm. 

 or more, and which are remarkably conspicuous in 

 compressed specimens. Occasionally also spines of 

 corresponding abnormal length are developed on 



Distal thecae as seen in bi-profilo view, ,i i • • -i • , i -i ■< / • ,1 • \ t ^ 



showing the rounded form of the tneC9e W m g immediately below (ninth pair), and also 



ES£ Ent^entTf P ;^of on tlie fourteenth pair (PI. XXVIII, fig. 2 6), but as a 



Pi. xxviii, fig. 2 e. ru ] e they are confined to the tenth pair alone. 



In this variety, also, the thecse usually number ten to eight in 10 mm., but 



occasionally, as in those from Mount Benger Burn, the thecse are a little more 



closely set. 



Horizon and Localities. — Hartfell Shales (zone of Pleurog. linearis). 

 S. Scotland : Hartfell; Mount Benger Burn. 

 Collections. — Lapworth and the Authors. 



Diplograptus (Orthograptus) Pageanus, Lapworth. Plate XXVIII, figs. 3 a — c. 



1873. Diplograptus Pageanus, Lapworth, nom. nudum, Geol. Mag., vol. ix, p. 134. 



Polypary relatively short, 2'5 — 4 cm. in length, typically somewhat fusiform 

 in shape ; widening from 2 mm. to a maximum breadth of 4*5 mm. 

 within 1 cm. of the proximal end, but diminishing again distally to a breadth 



Fig. 147.— Orthograptus Pageanus, Lapw- not exceeding 3 mm. TlieCEe sixteen to 



twelve in 10 mm. of the Orthograptus type, 

 furnished with loner horizontal and somewhat 

 flexed spines. 

 Description. — Although the more typical examples 



■ 



of the species are sub-fusiform in shape some examples 



Proximal end showing spinose nature sllOW little Or 110 tendency to liaiTOW towards the 

 of the thecse. Enlargement of part 



of pi. xxviii, fig. 3 a. distal extremity of the polypary. 



30 



