DIPLOGRAPTUS. 



241 



Horizon and Localities. — Lower Hartfell Shales (particularly zone of Dicranog. 

 GUngani). 



S. Scotland : Dobb's Linn, Hartfell ; etc. Ireland : Carnalea. 



Associates, etc. — 0. calcaratus is a common fossil in the Lower Hartfell Shales 

 in the zone of Dicranog. GUngani, where it occurs associated with Glimacog. bicomis, 

 Dicranog. ramosus, etc. Some individuals are also found in the underlying zone of 

 Glimacog. Wilsoni, but they are of rare occurrence. 



Collections. — Sedgwick Museum, Lapworth, and the Authors. 



Var. vulgatus, Lapworth MS. 



Plate XXX, figs. 5 a—d. 



Figs. 100 a — c. — Orthograptus calcaratus, var 

 vulgatus, Lapw. MS. 



E 



^.. j. 









1895. ? Diplograptus foliaeeus var. vulgatus, Peruer, G-rapt. de Boheme, pt. ii, p. 29, pi. viii, figs. 5 a — c. 



A well-marked variety of Orthog. calcaratus, which occurs abundantly in the 

 Lower Hartfell Shales, has been appropriately termed var. rid gal us. It differs 

 from the more typical form in three particulars : 



(1) In the absence of the extraordinary 

 development of basal spines ; 



(2) In the more abrupt widening and 

 general coarseness of the polypary ; 



(3) In the more everted character of the 

 apertural margin in subscalariform view. 



The polypary attains about the same length 

 as that of Orthog. calcaratus, but widens more 

 abruptly, and has in general a more coarse 

 appearance ; the widening from 1 mm. to 3 mm. 

 takes place within 1 cm. of the proximal end. 

 The tubular structure which probably contains 

 the virgula is even broader than in 0. calcaratus 

 as a general rule, but is occasionally seen to be 

 quite narrow, when it is probably the virgula 

 itself. 



The thecre are about the same in number 

 as in the typical form, but there is a tendency 

 to more distinct eversion of the apertural margin, accompanied by convexity 

 of the margin itself. This, as has been explained earlier, is probably due to the 

 more undulating character of the apertural margin itself. 



Small basal spines similar in position to those of Orthog. calcaratus are 

 developed as a rule, but they are always relatively inconspicuous. 



Horizon and Localities. — Lower Hartfell Shales, Dicranograptus Shales. 

 8. Scotland: Hartfell; Dobb's Linn, etc. Wales : Conway Railway Cutting; 



32 



a. Proximal end in sub-relief, obverse side as 



seen in sub-scalariform view. Note sicnla 

 and origin of septum. Dobb's Linn, Lower 

 Hartfell Shales (zone of Climacog. Wilsoni). 

 Coll. Lapworth. 



b. Obverse aspect, bi-profile view. Hartfell, 



Lower Hartfell Shales. Coll. Elles. 



c. Reverse aspect preserved as an impression, 



showing origin of septum. Hartfell Spa, 

 Lower Hartfell Shales. Coll. Geological 

 Survey of Scotland. 



