636 J. HOPKINSON AND c. lapworth ON THE GEAPTOLITES op 



Eoad Uchaf, where such an extensive and varied series of Grapto- 

 lites was discovered in 1872. Here the section Dendroidea is com- 

 pleted by the addition, to the three genera already enumerated, of 

 the somewhat remotely allied genus Ptilograptus ; and at least three 

 of the species from Whitesand Bay occur. 



Of the nine species of Cladophora from this locality, three, viz. 

 Dendrograptus diffusus, D. divergens, and D. jleocuosus, occur in the 

 Quebec Group of Canada, while the rest are new. The Rhabdophora 

 appear to come in here for the first time, and are represented by 

 three genera with six species, of which three, viz. Didymograptus 

 extensus, D. pennatulus, and Trigonograptus ensiformls occur also in 

 the Quebec Group, the others being new. 



From the occurrence amongst these fifteen species of three that are 

 found in the previously mentioned Whitesand-Bay beds, and of six 

 Quebec species, taken in connexion with the absence (so far as 

 known) of any Quebec species in the lower Whitesand-Bay beds, and 

 of their greater prevalence in the higher Arenig rocks of Whitesand 

 Bay and elsewhere, it would appear that we have here as early a 

 series of rocks as any known to be present in the Graptolite- 

 bearing portion of the Quebec Group, and perhaps a rather earlier 

 series. It may also be remarked that we have not yet a single 

 Skiddaw-Slate species. 



A somewhat similar fauna, with at least two identical species, 

 Dendrograptus diffusus and D.fiexuosus, has been discovered within 

 the last few years in the Arenig rocks at Shelve Church in Shropshire. 

 The species which occur here seem, however, more nearly allied to 

 those of the series next to be noticed, the Middle Arenig rocks of 

 Whitesand Bay. It is in these rocks that we have the first indica- 

 tion of an approach to the fauna of the Skiddaw series — the funicu- 

 late Dichograptidse, so fully represented in the lower beds of this 

 series, appearing for the first time in the St. -David's area in the 

 Middle Arenig rocks. Of the Rhabdophora, Didymograptus patulus, 

 Tetragraptus serra, and T. quadribrachiatus are common to the two 

 localities ; but the Cladophora, which are well represented here, are 

 very sparingly distributed in the Skiddaw area. 



This Middle Arenig subformation is even more nearly allied by 

 its Graptolites to the Point-Levis shales of the Quebec Group of 

 Canada, in which nearly all its species, both of Rhabdophora and 

 Cladophora, have been found. 



In the Graptolite zone of Shelve Church, already mentioned, many 

 of the species which occur low in the Middle Arenig series of St. 

 David's have lately been recognized. Didymograptus patulus, Ole- 

 matograptus implicatus, Dendrograptus diffusus, D. jleocuosus, Callo- 

 graptus elegans, and 0. Salteri are known in both localities*. 



* Didymograptus patulus and a Dictyonema were detected at this locality 

 by Mr. Morton of Liverpool some years ago (vide his " Greology of the Country 

 around Shelve," Proc. Liverpool Geol. Soc, Session 1868-69). The remaining 

 species noticed above, together with several additional forms, previously only 

 known to occur in the Skiddaw and Point-Levis beds, were discovered by Mr. 

 Hopkinson in 1872 and the present year (1874). 



