2 Hi 



BRITISH GRAPT0L1TES. 



Fiots. 166 a — e. — Orthograptus rugosus, 

 vnr. apiculatus, nov. 



r\ 









a. Proximal part of specimen in relief, 



obverse aspect, showing different 

 appearances of the thecee. Laggan 

 Gill, Girvan ; Ardwell Group. Geol. 

 Survey of Scotland. 



b. Proximal end, reverse aspect, with 



surface partly removed so as to show 

 complete sicula, and the origin of 

 septum. Enlargement of part of 

 PI. XXX, fig. 7 c. 



c. Reverse aspect showing origin of sep- 



tum. Laggan Gill. Geol. Survey 

 of Scotland. 



Fios. 166 d and e. — Orthoyraptus rugosus, 

 var. apiculatus, nov. 



> 

















7m 



Distal fchecse of a somewhat flattened 

 specimen, bi-profile view. Laggan 

 Gill ; Ardwell Group. Geol. Survey 

 of Scotland. 



Distal theca) of a slightly compressed 

 specimen showing the appearance 

 characteristic of Emmons' 1). rugosus. 

 ('American Geology/ pi. i, fig. 26.) 

 Ibid. 



with a short spine. Th. V 2 grows from th. I 1 nearly 

 horizontally across the back of the sicnla and then 

 bends somewhat abruptly to grow upward ; its aper- 

 ture also is slightly everted and spinose. The aper- 

 ture of th. 2 1 reaches the level of the apex of the 

 sicula, but like all the thecse developed after th. I 1 

 and th. I 2 this aperture is sub-horizontal and mucro- 

 nate, but not spinose. 



In the reverse aspect of the polypary nothing is 

 seen of the sicnla except its aperture and the virgella 

 (1 mm.), but the characters of the proximal thecse 

 are usually clearly visible. 



The thecae have an average length of 2 - 5 mm. ; 

 those nearest the proximal end show a slight ten- 

 dency to flowing sigmoid curvature, but distally, the 

 impressed edge of the polypary passes insensibly 

 into the free edge, and the curvature is practically 

 lost. The septal groove appears to originate 

 between the fifth thecal pair in the obverse aspect 

 and slightly lower down in the reverse. 



Affinities. — 0. rugosus, var. apiculatus, may be 

 regarded as standing midway between Orihog. calca- 

 ratu's, on the one hand, and Glyptog. teretiusculus 

 on the other ; the bi-profile view of the distal ex- 

 tremity shows a similar appearance to that presented 

 by 0. calcaratus, though the excavations are, perhaps, 

 somewhat more pronounced ; but in the proximal 

 region of the polypary the small amount of overlap 

 and the wide and deep excavations cause the 

 form to resemble closely in some aspects Glyptog. 

 teretiusculus. The more pronounced excavation and 

 width of the aperture relatively to the length of the 

 theca, should be sufficient to distinguish this form 

 from all the other members of the group. 



Horizons and Localities. — Upper Llandeilo and 

 Lower Bala (Balclatchie and Ardwell Groups). 

 Glenkiln-Hartfell. 



8. Scotland : Laggan Gill ; Ardmillan ; Pen- 

 whapple ; Piedmont Glen; Craigmichan Scaurs, etc. 

 Shropshire: Spy Burn. Wales : St. Clears (?). 



Associates, etc. — 0. rugosus, var. apiculatus occurs 



