DIPLOGRAPTUS. 



235 



bi-profile view, by the position of the spines on the proximal pair of thecas, and 

 by the absence or shortness of the distal prolongation of the virgula. 



Horizons and Localities. — Lower Hartfell Shales (zones of Dicranog. Cling am 

 and Pleurog. linearis). Harnage Shales. Whittery Ash. 



8. Scotland: Hartfell; Dobb's Linn; Myoch Bay, etc., etc. N. Ireland: 

 Ballygrot. N. Wales: Conway; Llanystwmdwy, near Criccieth. Shropshire: 

 Connd Moor Quarry ; Whittery Dingle, Soudley. 



Associates, etc.- — Orthog. truncatus is a common fossil wherever the Graptolitic 

 facies of the Bala-Caradoc rocks is developed, and is especially abundant in the 

 middle zones. It makes its first appearance in S. Scotland in the zone of 

 Dicranog. Clingani, where it swarms in association with the zone fossil, 0. 

 calcaratus var. basilicas, Dicellog. Morrisi, CI. caudafns, Dicellog. Forchammeri, and 

 other forms. It is abundant also in the P. linearis zone. 



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



In addition to the typical OrtJrog. truncatus there are certain other forms 

 which, while agreeing with it in the general type of theca, differ from it in the 

 size and shape of the polypary, and in minor thecal characters. Some of these 

 occur in association with the typical species, others upon horizons of somewhat 



earlier and later geological date. They 

 varieties. 



are here distinguished as separate 



Var. abbreviates, var. nov. 



Figs. 155 a, b, c, and d. — Orthograpius 

 truncatus, var. abbreviatus, nov. 



■ :/ 

 r 







d 



a. Fragment, obverse aspect, showing 



sicula. Dobb's Linn, Upper Hart- 

 fell Shales (zone of Dicellog. anceps). 

 Coll. Sedgwick Museum. 



b. Obverse aspect of more complete 



specimen on same slab. 



c. Eeverse aspect of another specimen 



on same slab. 



d. Distal theca; of another specimen on 



same slab. 



Plate XXIX, figs. 6 a—e. 



This variety is especially abundant in the Upper 

 Hartfell Shales. It is a small form, which appears 

 never to exceed 2 cm. in length. It has a maximum 

 breadth of 3 mm., so that it is relatively wide ; very 

 frequently this maximum breadth is attained a con- 

 siderable distance from the distal extremity, and 

 diminishes distally, giving a sub-fusiform appear- 

 ance to the polypary as a whole similar to that 

 typical of 0. truncatus itself. The thecal are, in 

 most respects, like those of the typical form, but 

 widen even more conspicuously towards the aper- 

 tural margin. The specimens are, as a rule, well 

 preserved, so that details of the structure of the 

 proximal end are clearly seen. 



Horizons and Localities. — Upper Hartfell Shales 

 and Lower Birkhill Shales (zones of Dicellog. 

 complanatus, D. anceps, Cephalog. acuminatus, and 

 Diplog. res ic u los us) . 



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



