134 



MR. H. LAPW0RTH ON THE 



[Feb. 1900. 



Horizon. — Zone of Monograptus Jtmhriatus, in the Gwa3taden 

 Series of the Rhayader District, with M.Jimbriatus, Nich., M. gre- 

 garius, Lapw., Climacograptus undulatus, Kurek., etc. 



Climacograptus extfemus, 



? Diploc/rapsus tere.tiusculus, His 



from -Jg- (normal) to 



Fig. 22 a. — Climacograptus 

 extremus, sp. nov. (nat. 



size). 



!i< 



p. nov. (Figs. 22 a & 22 b, a-e.) 



Richter, Zeitschr. Deutsch. Geol. Gesellsch. 

 vol. v (1853) p. 456 & pi. xii, figs. 11-13. 



Mature rhabdosoma. — The rhabdosoma has an average length 

 of T L- to 4- inch ; and in one case I have detected an abnormally 

 developed specimen having a length of t inch. The width varies 

 L inch. Above the rounded nose of the 

 proximal end the breadth usually 

 remains constant throughout the 

 rhabdosoma. The theca) alternate 

 regularly, numbering from 38 to 48 

 in the inch. The excavations about 

 the thecal apertures are unusually 

 small ; and, indeed, in many speci- 

 mens no excavations are to be seen. 



The chief characteristic of this 

 beautiful little graptolite is the 

 sutural groove which zigzags from 

 side to side, swinging from imme- 

 diately below the aperture of one 

 theca to a corresponding position in 

 the succeeding theca of the opposite 

 series. In well-preserved and in- 

 compressed specimens, the thecse are 

 seen presenting the appearance of a 

 pair of lips which completely en- 

 velop Ihe walls of the excavations 

 above the apertures. The external 

 margins of the thecge may be vertical, 

 or strongly concave. The thecal par- 

 titions are sometimes represented as 

 fine lines extending for a short dis- 

 tance below the mouth of the orifices. 

 Proximal end. — There does not 

 appear to be either an extension of 

 the virgella or prolongation of the 

 nor in any of my examples have I been able to trace a 



a = Abnormally long specimen. 

 />-^ = Kormal examples. 



22 b. — The same ( x 5). 



Fig. 



irgula 



sign of a sicula : possibly it may be enveloped within the primary 

 thecoe. 



This species differs from Climacograptus undulatus, Kiirek. in 



(1) The size of the rhabdosoma ; 



(2) The characters of the proximal end ; and 



(3) The form of the thecas. 



From Diplograptus IJughesii, Nich., to which it bears a certain 

 resemblance, it may be distinguished by 



(1) The width of the rhabdosoma ; and 



(2) The form and length of the thecae. 



