Mr. C. Lapwortli on new British Graptolites. 169 



in their middle portion over the mouth of the preceding theca, 

 while the apertural portion is wide and patulous. The speci- 

 mens preserved in partial relief show that the thecal walls 

 of each series are prolonged in a distinct groove into the 

 central portion of the polypary, as in the last-mentioned 

 species ; so that in casts the impressions of the thecaj present 

 the imbricated or amplexicaul arrangement so marked in D. 

 perexcavatus and D. amplexicaulis. 



This form is frequently confounded with Diplograptus 

 foliaceus, Murch., from which it differs (a) in the smaller in- 

 clination of the hydrothecEe, (b) their greater distal expansion 

 and (c) imbricate arrangement, and (d) in the shape and pro- 

 longation of the apertural margin. 



I have provisionally referred it to Diplograptus rugosus y 

 Emmons, which was the earliest described example of the 

 American species figured under the references given above. 

 Of the specific identity of all these forms it is as yet impossible 

 to speak with certainty ; but those figured can all be paralleled 

 by Girvan examples of the form under description. 



Horizon and Locality. Diplograptus mgosus is a very com- 

 mon form in the Lower Girvan rocks (Bala) of Laggan, Ard- 

 millan, Penwhapple, Piedmont Glen, &c. Examples doubt- 

 fully referable to the same species have been collected by 

 myself from St. Clears and other Welsh localities. 



26. CHmacograptus confertus, Lapw. 

 (PI. IV. figs. 15 «, 15 b, 15 c.) 



Climacograptm confertus, Lapwortli, Quart. Journ. Geol. Soc. 1875, 

 pi. xxxiv. figs. 4 a-f. 



This species has been already figured and described ; but, 

 owing to the absence of perfect specimens, the original drawing 

 and diagnosis were very imperfect. The figures given in the 

 present plate are drawn from more complete specimens re- 

 cently collected by myself from the Lower Llandeilo beds of 

 the neighbourhood of Llan Mill, near Whitland. The lateral 

 spines characteristic of C. cwlatus are not present in this 

 form. There is a distinct distal prolongation of the virgula. 



G. confertus is closely allied to the species C. ccelatns, 

 Lapw., and ranges apparently from the Upper Arenig to the 

 summit of the Llandeilo formation. 



Idiograptus, subgen. nov. 



Polypary diprionidian, with concavo-convex section, zigzag 

 septum, and subcentral, filiform, direct virgula. Hydrothecse 

 consisting of alternate overlapping flattened prisms, contract- 



