DIPLOGRAPTUS. 



257 



Horizon and Localities. — Llandovery, Skelgill Beds (zones of M. fimbriatus, 

 M. argenteus.) 



Lake District : Skelgill ; Troutbeck Valley ; Mealy Gill ; Swindale Beck, 

 Knock, etc. 8. Scotland : Dobb's Linn. Wales : Llanystwnulwy, near Criccieth ; 

 Rhayader. 



Associates, etc. — G. sinuatus occurs in some profusion in the Skelgill Beds of 

 the Lake District in the zone of Monog. fimbriatus ; it is beautifully preserved in 

 relief, and occurs with Glimacog. Hughesi, 01. recta/ngularis, 67. Tornquisti, 

 Monog. fimbriatus, and other forms. It is also found in the zone of Monog. 

 argenteus associated with the zone fossils. It is rarer in S. Scotland. 



Collections. — Sedgwick Museum, British Museum (Nat. Hist.), Marr, Fearnsides, 

 Lapworth, and the Authors. 



Diplograptus (Glyptograptus) persculptus, Salter. 



Plate XXXI, figs. 7 a — c. 



Figs. 176 a and b. — Glyptograptus per 

 sculptus, Salter. 



1868. Diployrapsus persculptus, Carruthers, Geol. Mag., p. 130. 



1873. Biplograpsus persculptus, Salter, uom. nudum, Cat. Fossils, Mus. Pract. Geol., p. 25. 



Polypary 3 cm. or more in length, widening quickly to a maximum breadth of 

 2 to 2*5 mm., which is thereafter maintained. Sicula conspicuous, with 

 small virgella. Tkecas ten to eight in 10 mm., long tubes with axes 

 twisted, and with decided sigmoid ventral curvature, 2 mm. in length, 

 overlapping one half, and with apertural margins slightly undulate ; 

 everted in profile view. 

 Description. — The only examples of this species known to us are preserved in 

 a state of semi-relief. The polypary presents an appearance somewhat similar to 



that noted in the case of Glyptog. sinuatus, but the 

 torsion of the thecas seems to have been much more 

 pronounced. The polypary itself widens gradually 

 from 1 mm. to a maximum of 2 to 2*5 mm., which 

 is attained within 1*5 cm. of the proximal end. 

 The sicula, when completely visible in young- 

 stages, measures 2'1 mm., but of this length 

 not much more than 1 mm. is usually visible in 

 the obverse aspect of the adult polypary. Th. I 1 

 originates at a point about *5 mm. above the aper- 

 ture of the sicula, and grows at first straight 

 downward until it is some little distance below 

 the level of the sicula, when it bends abruptly 

 round and grows upward and, but very slightly, 

 outward. Th. I 3 grows upward and outward from it 

 on the opposite side of the sicula in such a manner that it leaves the sicula free 



34 



a. Obverse aspect, in relief showing 



sicula. Gogofau, Carmarthen, Llan- 

 dovery Beds. Coll. Brit. Museum 

 (Nat. Hist.). 



b. Reverse aspect, in full relief showing 



the twisting of thecal axis. Ibid. 



