244 BRITISH GRAPTOLITES. 



Var. priscus, var. now Plate XXX, figs. 6 a — c. 



1875. Diplograptus foliaceus, Lapworth, Quart. Journ. Gcol. Soc, vol. xxxi, p. 657, pi. xxxv, figs. 

 7 a— 7 g. 



Another form, Avhich may provisionally be regarded as a variety of Orthog. 

 calcaratus, occurs in abundance in the Llandeilo rocks of S. Wales. 



It is very long— occasionally reaching 12 cm. in length — and widens gradually 

 to 5 mm. from 2'5 mm. at the proximal extremity, which is broad and abrupt; the 



ventral margins are, however, parallel for the greater 



Fig. 101. — Orthograptus calcaratus, var. . . <> , , . -, . •■ ml . , . . , -, , , 



priscus, nov. portion of their length. Ihe sicula is embedded and 



\ |S 



has a stout and short virgella; the two proximal 

 thecee are adorned with small, but conspicuous, 

 V apertural spines. 



The thecae number fourteen to ten in 10 mm. : 



Y | J* they have a length of about 3 mm. and overlap one 



* half to two thirds of their extent. They are, as it 



\ were, somewhat pressed inwards towards the axis 



Distal thecffi Enlargement of part of Q f t ] ie po lypary, SO that ill bi-profile view the 

 PI. XXX, fig. 6 a. r J r « ' *■ 



apertural margin projects but slightly from the 

 ventral edge. In sub-scalariform views, however, there is presented a well- 

 marked sub-mucronate denticle. 



Remarks. — Var. priscus is the Llandeilo form that was referred by Lapworth in 

 1875 to Diplog. foliaceus, Murch., and which at that time (supra, p. 657) appeared 

 to him to be identical with the form figured and referred by Hall in his ' Palaeon- 

 tology of New York,' vol. i, pi. lxxii, figs. 2 a — c, to Fucoides secalinus, Eaton. 

 It seems, however, advisable to drop Eaton's name altogether in view of the 

 impossibility of determining the original form of the distorted examples to which 

 Eaton applied it. 



Affinities. — Var. priscus is characterised by its size and by its adpressed thecas, 

 which are small and closely set in the proximal region of the polypary. These 

 features, together with the broad proximal end, serve to distinguish it from all 

 other varieties of Orthog. calcaratus. 



Horizons and Localities. — Llandeilo (zone of Didymog, Murchisoni) ; Glenkiln 

 Shales (zone of Dicellog. patulosus). 



8. Wales .• Abereiddy Bay, Pembrokeshire ; Drefach, Mydrim, St. Clears. 

 N. Wales ■. Tiddyndicwm. 8. Scotland (?) .- Glenkiln Burn (?) ; Craigmichaii 

 Scaurs (?). 



Associates, etc. — Var. priscus is a common fossil at Abereiddy Bay in the zone 

 of Didymog. Murchisoni, where it occurs associated with Didymog. Murchisoni, 

 Mesog. cuiatus, and Gryptog. tricomis. The occurrence of var. priscus in S. 



