160 PEor. o. T. JOXES ON [vol. Ixxvii, 



appear in the Cartlett Beds, and are characteristic of the greater 

 part of the Haverford Stage. 



In Scotland there is also found in the Woodland Beds a faintly- 

 ribbed form which Dr. F. li. C. Keed refers to a variety of Strick- 

 landinia lirata, and is not unlike one that occurs near the top 

 of the Millin Stage. Unfortunately, the nomenclature of the forms- 

 of this D'enus is very unsatisfactory and needs revision. Dr. Beed,^ 

 in following Davidson, has perpetuated the existing confusion. 



The Strophomenida:^, represented by Sirojjhomena, Sfroj^heo- 

 clonta, SchuclierteUa, and other subgenera, are especially charac- 

 teristic of the Woodland Beds, and the forms are closely analogous 

 to those of the Gasworks Beds, although some of the latter appear 

 to occur also in the Mulloch-Hill Beds. The most distinctive 

 feature of the Haverford Stage is the abundance of forms of JPJect- 

 amhonitfs which are allied to P. dupJicatiis. The typical species 

 occurs in swarms at the to^) of the Gasworks Mudstones ; but in the 

 lower parts of the stage Avell-marked varieties can be distinguished. 

 It is possible, in fact, to use these forms to some extent as zonal 

 indices. The genus is also represented in the Woodland Beds by 

 swarms of individuals wdiich agree in their stage of development 

 with those of the lower part of the Gasworks Mudstones ; while 

 the presence of a few specimens of the typical form indicate an 

 approach to the horizon at the top of the mudstones. Dr. Keed 

 has erroneously referred these to PJectamhanites transversal is^ 

 which is readily distinguishable from all forms of -P. duplicaius, 

 and is distinctive of the AVenlock rocks. 



It is impossible, when comparing the brachiopod fauna from these 

 distant localities, not to be impressed by the great resemblance 

 between the Woodland fauna and that of the Gasworks Mudstones. 

 There a]'e, however, undoubtedly some forms in common with the 

 Mulloch-Hill fauna ; vdiile the species ascribed by Dr. Reed to 

 StricJdandinia lirata, var. scofica would seem to indicate a more 

 advanced development than is shown by any of those from the 

 Haverford Stage. 



The majority of the forms of Pliacops in the Haverford Stage 

 may be referred jDrovisionalh' to PJi. elegans Sars &, Ba?ck, wliile 

 others are intermediate between that species and Pit. stol'esi Milne 

 Edwards. The specimens from the Woodland Beds are identical 

 with those which occur commonly in the Gasworks Mudstones. 

 The Mulloch-Hill species seem to be specifically distinct, and have 

 not been observed in the Haverfordwest district. 



Again, the forms of the latter district are closely matched in the 

 Middle and Tapper Skelgill Beds of the Lake District, correspond- 

 ing to the 3f.-Je2?totheca and M.-convoJtitus Zones. 



The distribution of the species of Tliacops thus confirms the 

 impression conveyed by the more abundant brachiopods, and the 

 correlation of the Woodland Beds with the main part of the Gas- 



^ ' The Ordovician & Silurian Brachiopods of tlie Girvan District ' Trans. 

 Eoy. Soc. Edin. vol. li (1917) p. 795. 



