DIPLOGRAPTUS. 



243 



Figs. 162 a and b. — Orthograptus cal- 

 caratus, var. basilicus, Lapw. 



Var. basilicus, Lap worth. Plate XXX, figs. 2 a — d. 



1873. Orthograptus basilicus, Lapwortli, mm. nudum, Geol. Mag., vol. x, p. 134. 



Another variety of Orthog. calcaratus is of common occurrence in the Lower 

 Hartfell Shales. Like the foregoing varieties, var. hasilicus is distinguished from 

 the typical form by the absence of prominent basal spines. It is a narrower and 



more compact form than either var. vulgatus or var. 

 acutus, and the thecsB project less from the margin of 

 the polypary. The average breadth does not exceed 

 2'5 mm., and this is attained somewhat rapidly 

 from an initial breadth of about 1 mm. within 1 cm. 

 of the proximal end. The thecse number eleven 

 to nine in 10 mm ; they have an average length of 

 3 mm., and overlap one half their extent; the 

 basal theca? have small spines only. The sicula is 

 2 mm. in length. The septal groove seems to 



I 



' 



a. Sicula and theca l 1 . On same slab 



as PI. XXX, figs. 2 c and 2 d. 



b. Proximal end of adidt example, ob- 



verse view. Enlargement of part originate between th. 4 1 and th. 3 2 . 



of PI. XXX, fig. 2d. rt 



Horizon and Localities. — Lower Hartfell Shales 

 (zones of Dicranog. Glingani and Plenrog. linearis). 



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



Associates, etc. — Var. basilicus occurs in fair abundance in the zones of Dicranog. 

 Glingani and Pleurog. linearis, associated with the zone fossils, Orthog. truncatus, 

 var. pauperatus, and other forms. 



Collections. — Sedgwick Museum, Geol. Survey of Scotland, Lapwortli, and the 

 Authors. 



Var. tenuicornis, var. nov. Plate XXX, figs. 4 a — c. 



Figs. 103 a and b. Orthograptus cal- 

 caratus, var. tenuicornis, nov. 













/ 



' 



a. Sicula and thecal l 1 and I s . On same 



slab as PI. XXX, figs. 4 a and b. 



b. Proximal end of adult specimen. 



Enlargement of part of PI. XXX, 

 fig. 4 a. 



This variety is closely allied in thecal characters 

 to the type. The basal thecse are furnished with 

 two long, slender, apertural spines, Avhich may have 

 a length of fully 7 mm., but the virgella is short 

 and inconspicuous. The virgular tube also is 

 generally very slender, while the general form of 

 the polypary recalls that of var. vulgatus rather 

 than that of Orthog. calcaratus itself. 



Horizon and Localitij. — Lower Hartfell Shales. 



8. Scotland : Morroch Bay, two miles south of 

 Portpatiack. 



Collection. — Geological Survey of Scotland. 



