Mr. C. Lap worth on new British Graptolites. 167 



Few of the specimens of this form exceed an inch and a half 

 in extent ; but occasionally a group of gigantic examples are 

 met with three or four inches in length. The margins are 

 perfectly parallel throughout, except near the proximal ex- 

 tremity, which is rounded off and provided with a short radicle 

 only. In the generality of examples the virgula is prolonged 

 distally to an extent almost equal to that of the polypary 

 itself. The hydrothecas are of the form of those of Diplo- 

 graptus tamariscus, Nich. (the type of the subgenus Glypto- 

 grap>tus) . They are rounded tubes, approximately of the same 

 diameter throughout, and divided from each other by a non- 

 polypiferous internode equal to their own length. They are 

 arranged in alternating order on a polypary of concavo-con- 

 vex (?) section, with no visible septum upon the reverse aspect, 

 but with a thick continuous test, which is strongly striated 

 transversely. 



This species differs from the Arenig form referred by authors 

 to Brongniart's Diplograptus dentatus (to which I formerly 

 assigned it) in several important points of structure. In some 

 good examples of that form, lately procured by myself from the 

 Arenig beds of Shelve, the thecal overlap for half their length, 

 their edges are undulating, and the proximal extremity of the 

 polypary is provided with three spines. 



Horizon and Locality. Diplograptus euglyphus is rare in 

 the Glenkiln Shales of Dobb's Linn, Craighmichan, Hart- 

 fell, &c, but very common in the Glenkiln beds of Birnock, 

 Cairn Hill, &c. in the Leadhills district. 



24. Diplograptus perexcavatus, Lapw. 



Climacogrceptus perexcavatus, Lapwortli, Trans. Belfast Nat. Field- 



Club, 1877, pi. vi. figs. 35, a, b. 

 Diplograptus angustifolius, Hall, Lapwortli, ibid. figs. 1, a, b. 



In the Glenkiln and Lower Hartfell Shales of the south 

 of Scotland one of the commonest fossils is the diprionidian 

 Graptolite named above. I have hitherto ranged it indifferently 

 in Climacograptus and Diplograptus, from the circumstance 

 that it exhibits the distinct characteristics of these genera 

 combined in one and the same polypary. I have recently 

 collected several examples of this form in partial relief. The 

 evidences they afford of its general structure permit us to 

 remove it from Climacograptus, and to range it definitely 

 under Diplograptus, from the type forms of which, however, 

 it differs so greatly that it ought probably to form the type of 

 a distinct subgenus. 



In the obverse aspect (PI. V. figs. 25 b, 25 c } 25 d) the 

 hydrothecse show all the characteristic features of those of 



12* 



