Vol. 56.] SILURIAN SEQUENCE OP RHAYADER. 131 



will become, in time, the standard by means of which future geo- 

 logists will unravel even the tantalizing complex of Central Wales, 

 and bring into line the many scattered and isolated patches of the 

 Handover}^ and Tarannon rocks which surround it. 



In conclusion, I wish to express my indebtedness to Prof. W. W. 

 Watts, M.A., Sec.G.S., who has furnished me with descriptions 

 of microscopic slides of the various local rocks ; to Mr. C. A. 

 Matley, B.Sc, F.G.S., for the identification of the greater number 

 of the brachiopoda which have been obtained from the district ; 

 and to my former colleagues, Mr. W. S. Becher, A.M.I.C.E., and 

 Mr. G. Waterhouse, Stud. Inst. C.F., for occasional assistance. I am 

 personally responsible for the identification of the graptolites ; but 

 a few doubtful species were referred to Miss E. M. E. Wood. 

 Finally, the continued interest of my father, Prof. C. Lapwortb, 

 F.lt.S., has greatly encouraged me in carrying out the researches 

 described in this paper. 



IV. Appendix. 



On New Species of Graptolites from the Rhayader District. 



The following new species of graptolites have been detected in 

 the course of my investigations in the field. While recognizing 

 the evil effects which result from the straining of minute palseonto- 

 logical distinctions to an excessive degree, and the introduction of 

 new forms, many of which are useless and unnecessary, I am of 

 opinion that the species described below are so distinctive in their 

 peculiarities, and so characteristic of certain zones in the Rhayader 

 district, that they deserve an introduction into the society of 

 recorded species. They form in every case the predominant fossils 

 of their own particular zones. For this reason, the descriptions of 

 these graptolites may be of use to future investigators in Central 

 Wales ; useful, perhaps, when they are the only fossils obtainable, 

 and at a time when one must perforce be content with the few gifts 

 of this kind which Nature has provided. 



CLiyiACOGSAPTUS pakvulus, sp. iiov. (Figs. 20 a & 20 b, p. 132.) 



Mature rhabdosoma. — The rhabdosoma rarely exceeds yL to 

 A inch in length, with an average breadth of about -^ inch. The 

 thecae number from 4 to (3 in the length of the rhabdosoma, and 

 are at a distance of ■£% to ^ inch apart. They are somewhat 

 similar to those of the Climaeograptus scalaris-tyipe. The excavations, 

 however, seem relatively larger, the vertical or slightly inclined 

 exterior margins occupying only about half the distance between the 

 adjacent apertures. Thevirgula is completely visible in the obverse 

 aspect : it does not, however, appear to be prolonged beyond the 

 youngest thecse. 



Proximal end. — The sicula attains a length of about -^L inch. 

 Its dorsal wall is free for about one-fourth to one-third of its 



k 2 



