228 BEITISB GRAPTOLITES. 



slender nature of the spines ; from such a species as Orthog. quadrimucronatus it 

 differs in the more upward direction of its spines and their greater length relatively 

 to the length of the polypary . 



In the general characters of the thecal and ornaments 0. Whitfieldi bears a 

 certain resemblance to the Glossograptidse. 



Horizon and Localities. — Glen kiln Shales, and equivalents. 



8. Scotland: Glenkiln Burn; Belcraig Burn; Dobb's Linn, etc. N. Wales: 

 T iddyn die wm ; Pensiflog. Central Wales: B nil th Road. 



Associates, etc. — Orthog. Whitfieldi is fairly common in a fragmentary condition 

 wherever the Glenkiln Shales are found. It is usually associated with Nemag. 

 gracilis, Dicellog. sextans, Glimacog. Scharenbergi, Amplexog. perexcavatus and other 

 forms. Complete specimens are rare. 



Collections. — 'Geological Survey of Scotland, Lapworth, and the Authors. 



Diplograptus (Orthograptus) insectiformis, Nicholson. Plate XXVIII, figs. 7a — c. 



1869. Diplograpsus insectiformis, Nicholson, Ann. Mag. Nat. Hist. [4], vol. iv, p. 237, pi. xi, fig. 13. 



1876. DijjlograjAus insectiformis, Lapworth, Cat. West. Scott. Foss., pi. ii, fig. 40. 



1877. Diplograptus insectiformis, Lapworth, Grapt. Co. Down, pi. vi, fig. 15. 



Polypary typically small, not exceeding 1 cm. in length, with an average 

 breadth of 1'5 mm. attained by gradual widening from the proximal end. 

 Sicula relatively large. Thecae twelve to ten in 10 mm., of the general 

 Orthograptus type, but slender, with a length of 1*5 mm. overlapping one 



half to two thirds of their extent ; apertural 



Figs. 150 a, b and c. — Orthograptus in- _ 



secti/urmis, Nich. margins slightly lobate, prolonged into deli- 



cate flexed spines. 

 Description. — The polypary in Orthog. insecti- 

 formis is usually small, and it has a characteristic 







i 



■ 



gregarious habit. Occasionally, however, solitary 

 specimens are found which are usually somewhat 

 larger; these may have a length of 2 cm. and a 



r 





breadth of 2 mm. 



The sicula is relatively large, measuring fully 2 



mm. in length ; it reaches up to the level of the aper- 

 ture of th. 2 2 . Th. I 1 grows straight upward and Out- 

 fit. Proximal end, reverse aspect, showing , . 



sicula and long apertural spines, ward from near its aperture ; th. P grows obliquely 



Dobb's Linn, Lower Birkhill Shales „ . n . . - „ „ « ,, 



(zone of m. gragarius). Coii. Eiies. from it so as to leave the sicula tree tor tuily one 



b. Young specimens, obverse aspect, .-, ■ 1 ., n ,, • n ml , 



showing fun length of sicula. ibid, third its length on one side. I he septum is mcom- 



c. Distal thecoe, sub-scalariform view. t , ,i i • p •, • ,i .„„„„„ „ „„+. 



Enlargement of part of ri. xxvm, piete, there being no sign oi it m the reverse aspect 

 g ' 7 b ' of the polypary. 



Affinities. — The only other spined Diplograptid with which 0. insectiformis 



