THE ARENIG AND LLANDEILO ROCKS OP ST. DATID's. 655 



more rigid than in the typical form. A single specimen only has 

 been procured from the Upper Arenig shales of Llanvirn ; and this, 

 in some of its characters, points in the direction of the very distinct 

 D. Forchhammeri. This unique specimen is of very great interest, 

 as it is the earliest example yet detected of the family of the 

 Dicranograptidse . 



Loc. Upper Arenig, Llanvirn Quarry. Middle Llandeilo, Aber- 

 eiddy Bay. 



Family DIPLOGEAPTID^E, Lapworth. 

 Genus Climacograptus, Hall. 

 Climacograptus cjslatus, Lapw., sp. nov. PI. XXXV. figs. 8 a-& e. 



Length from one inch to one inch and a half, maximum width one 

 eighth of an inch, ventral margins normally parallel, but rapidly 

 converging towards the proximal extremity, which is abrupt and 

 furnished with two short horizontal spurs; virgula stout, 

 greatly prolonged both proximally and distally; hydrothecse 

 20 to 24 to the inch, apertural margins concave, very oblique ; 

 interspaces deep, and occupying about two fifths of the ventral 

 margin. 



The prolonged proximal portion of the virgula frequently attains 

 an extraordinary length in this species, sometimes equalling that of 

 the polypary itself. It is often expanded a little in the centre of 

 its length, but it never forms any thing deserving the title of ter- 

 minal vesicle. The radicular spurs are stout and short, and are 

 often very rudimentary. Perhaps the most marked characteristic 

 of the species is afforded by the peculiar shape and direction of the 

 interspaces, the proximal boundary of each, instead of being hori- 

 zontal as in all the more recent Climacograpti, makes an angle of 

 about 60° with the general axis of the polypary. This is in all 

 likelihood due to the circumstance that the section of the uncom- 

 pressed polypary was somewhat concavo-convex, the distal end of 

 each theca at the same time being a little introverted, as in the sub- 

 genus Glyptograptus. A similar appearance is noticeable in the 

 following species (O. confer tus). 



Loc. Lower Llandeilo, Abereiddy Bay (lower zone). 



Climacograptus confertus, Lapw.,sp. nov. PI. XXXIY. figs. 4a-4f. 



Length about one inch, maximum width one twelfth of an inch, 

 margins parallel ; proximal extremity pointed, furnished with 

 a short radicle only ; hydrothecse about 40 to the inch ; inter- 

 spaces subtriangular, slightly oblique, and occupying about one 

 third of the ventral margin. 



The distinguishing peculiarities of this small species are its 

 diminutive size, the absence of distal prolongation of the virgula, 

 and the remarkable form and proportions of the interspaces. The 



a J. G. S. No. 124. 2 x 



