NICHOLSON SKIDD AW GRAPTOLITES. 139 



17. DiPLOGRAPSIJS ANTENNARIUS, Hall, Sp. 



Climacograpsus antennarius, Hall, Grapt. Quebec Group, p. 112, 

 pi. 13. figs. 11-13. 



I have obtained several specimens of this remarkable species from 

 the slates at Outerside, but their preservation is seldom good, as 

 far as regards any part but the base. The frond is simple and 

 quadrangular, celluliferous on the two sides, and having the axis 

 extended beyond its distal extremity, sometimes for more than ^ 

 an inch. The length of the frond varies from -J- of an inch, the 

 smallest observed, to |- of an inch, exclusive of the axis ; and the 

 average breadth is one line. The most peculiar and characteristic 

 part of this Graptolite is the base, which is adorned with three pro- 

 cesses. Of these, the middle one is a small triangular extension of 

 the axis, the true " radicle ; " and the two lateral ones are long, 

 setiform, straight or curved processes, springing from the lateral 

 angles of the base, and sometimes attaining a length of -} of an 

 inch, the two including an angle of about 120°. All my specimens 

 are simply imperfect scalariform impressions ; but, according to Hall, 

 the cellules, which are excavated in the substance of the stipe, are 

 from 24 to 28 in an inch, " short, nearly twice as wide as long; the 

 cell- denticles nearly rectangular to the axis." 



Loc. Outerside, near Keswick. 



18. DiPLOGRAPSUS MUCRONATUS, Hall. 



Graptolithus mucronatus, Hall, Pal. New York, vol. i. p. 268, pi. 73. 

 figs. 1 a-d. 



Three specimens of this species have come under my notice from 

 the Skiddaw Slates, though I believe it has not been before observed 

 to occur below the horizon of the Upper Llandeilo rocks either in 

 Britain or in America. The frond is bicelluliferous ; the cellules 

 25 to 30 in the space" of an inch ; the denticles slender, prominent, 

 and extended into flexible mucronate tips. The axis is usually pro- 

 longed beyond the distal extremity of the frond ; but the nature of 

 the base is not known. 



Loc. Outerside, near Keswick. 



19. DiPLOGRAPSUS TERETII7SCT7LUS *, His. PL Y. figS. 11-13. 



This species is essentially an Upper-Llandeilo form, though it has 

 recently been discovered by Prof. Harkness in the Lower Llandovery 

 rocks, near Haverfordwest, in Wales (Geol. Mag. vol. iv. no. 6). It 

 was first noticed as occurring in the Skiddaw Slates by Prof. Hark- 

 ness and myself (see Quart. Journ. Geol. Soc. vol. xxii. p. 480) ; so 

 that it is now known to range from the Lower Llandeilo to the 

 Lower Llandovery rocks, though it is apparently confined to the 



* J), teretiusculus, His., and B. antennarius. Hall, with some other species, 

 belong to a section of the Lijplograpsi in which the cellules are simply excavated 

 in the substance of the stipe. Hall has placed these in a distinct genus vmder 

 the name of Climacograpsus ; and it woiild seem advisable in future to accept 

 this change, though the old names have obtained such a general currency. 



