156 



BRITISH GRAPTOLITES. 



slight concave curve near the proximal end, changing distally, however, to a 



convex one. 



They measure 



6, and c. — Dicellograptus 

 Morrisi, Hopk. 



a. Proximal end showing- typical rounded 

 form of axil. Hartfell Spa, Hart- 

 fell Shales. Coll. Wood. 



6. Ditto, showing mesial spines. Speci- 

 men on same slab as PI. XXI, fig. 66. 



c. Young specimen showing nema and 

 apex of sicula. On same slab as 

 PI. XXI, fig. 6d. 



•5 mm. at their origin and widen fairly rapidly to 

 a breadth of 1*3 mm. ; there is little or no further 

 increase in width after the first 2 — 3 cm., however 

 long the stipes may be. 



The sicula is short and narrow, and measures 

 1*5 mm. in length ; its apex is, however, frequently 

 broken off, and then it appears as a blunt pro- 

 tuberance within the axil. The earliest developed 

 theca? are wide, giving a thickened look to the 

 proximal end as a whole. The virgella and lateral 

 spines are thick. The axil is characteristically 

 round, and does not present the square appearance 

 of that of many other Dicellogra/pti, as, for example, 

 D. elegans. 



The thecae are more closely set in the proximal 

 than in the distal region, where they have an 

 average length of 2 mm. All the proximal thecas 

 have mesial spines. When preserved in true profile the free part of the outer 

 wall is oblique and curved or crenulate, but in certain specimens where the stipes 



are somewhat twisted, this wall appears nearly 

 straight. The ventral excavation often appears 

 to be completely filled by the introverted thecal 

 aperture. 



u:\ffitities. — ]J. Morrisi resembles D. Forchammeri 

 in the general characters of its theca), but it differs 

 from it in its smaller axillary angle and in its mode 

 of growth. It approaches most nearly to IK moffa- 

 tensis, but it is a less robust form, the stipes are 

 more uniform in width throughout, and the axil is 

 more open and rounded. 



Horizon and Localities. — Lower Hartfell Shales 

 (zone of I). Clingani and Pleurog. linearis) ; Ard- 

 millan Beds (Bala) of Girvan. 



8. Scotland.— Moffat Area : Dobb's Linn ; Hartfell 

 Spa ; Garryhorn Burn ; Belcraig Burn. Girvan Area : Myoch Bay ; Penwhapple 

 Burn, etc. Ireland: Bynehill; Carighalea ; Tramore, Co. Waterford. 



Associates, etc.— J). Morrisi is an extremely abundant fossil in the zone of 

 D. Clingani and P. linearis, and it sometimes occurs in such numbers as to exclude 

 all other forms. It is often, however, found associated with D. Clingani, Diplog. 

 foliaceus (auet.), and Diplog. truncatus. 



Figs. 98<Zand< 



—Dicellograptus Morrisi, 

 Hopk. 



l A 



Distal thecae, profile view. Enlarge- 

 ment of part of PI. XXI, fig. 66. 



Thecae, various aspects. On same 

 slab as PI. XXI, fig. 6 6. 



