166 

 EXPLANATION OF PLATE VIIL* 



1. Rastrites peregrinus, Barr. (original, from Moffat). 



2. Graptolithus priodon, Broun (a, from Murch. Siluria; b, d, and e, Geinitz, 

 Die Grapt- ; c, Carr., Intel. Obs., vol. xi.). b, side view of the polypary; 

 d, back view sliowing solid axis partly removed; c, intermediate position ; 

 and e, front view, showing a section of the common canal and axis . 



3. G. Hismrjeri, Carr. = G. Sagittarius, His. non Linn, (a and c, Nich., Geol. 

 Journ., vol. xxiv. ; b, original, from Builth). 



4 O. Sedgwickii, Portl. var. (original, from Aberystwith). Associated with 

 this species I have found fragments of G. priodon and of G. Bisingeri. 

 From this I am induced to assign the rocks of Aberystwith to the Caradoc 

 formation. The geological survey place them in the Llandovery. No 

 fossils, except worm tracks, have previously been recorded from here. 



5. Cyrtograpsv-S Murchisoni, Carr. (Carr, Geol. Mag., vol. vii.) This species 

 is only known to occur at Builth, where I have found specimens. 



6. Didymograpsus MurcMsoni, M'Coy (a, original, from Llandrindod, Builth; 

 b, Baily, Brit. Foss., slightly altered). 



7. Tetragrapsus hryonoidcs, Salt. (Hall, Grapt. Queb. Group). 



8. Bicliograpsus octdbrachiatus, Hall (Hall, op. cit.) . With corneous disc. 



9. Cladograpsus linearis, Carr. (a, Murch. Sil., ed. iv. ; b, Carr., Int. Obs.). 



10. Dendrograptus Hallianus, Prout. iHall, op. cit.) 



11. Biplograpsus pAstis, His. (a, Carr., Geol. Mag., vol. vii ; b, enlargement of 

 a narrower specimen, original, from Moffat). 



12. J), penna, n. sp. (original, from Moffat). The fracture shown at c, must, I 

 think, have taken place during the deposition of the sediment in which this 

 curious specimen is preserved. 



13. D. folium, His., a young specimen (original, from Moffat). 



14. Cephalogra^isus cometa, Gem. B'p. (a, and c, Carr., op. cit.). The enlarged 

 figure is intended to show the general structure of the polypary. I have 

 not examined the species microscopically, and therefore cannot say that this 

 drawing is quite cerrect. 



15. Climacograptus scalaris, Linn, et Hall (a, Carr , op. cit. ; b, c, and d, 

 original, from Moffat). The enlarged figures show the different positions in 

 which this species is preserved. 



16. C. hicornis, Hall (Hall, op cit.). c, the proximal end of a young specimen 

 showing a well developed radicle, X 2 dia ; d, the proximal end enveloped 

 in a corneous disc. 



17. Dicranograpitus ramosvs, Hall (op. cit.). At b, the pustules referred to, are 

 shown ; and on the left of c, are the axiertures of the hydrothecse. 



18. Phyllograptus angustifolitis, Hall (op. cit.). 



19. Diagram showing the structure of the genus Climacograptus (Hall, op. cit.), 



X 8 dia. The division between the hydrothecse separates them entirely 

 until it approaches the axis, when it gradually becomes narrower, allowing 

 the csenosarc to communicate freely between all the polypites. 



20. Horizontal section showing the structure of the genus Phyllograptus (op, cit.). 



21. Young specimen of Climacograptus (original, from Moffat). 

 22 — 25 Germs of various species ^original, from Moffat). 



26. Young specimen of Biplograpsus tricornis (CaiT., Int. Obs., vol. xi.). 



27. Germ of a diprionidian species. No hydrotheca> apparent (Hall, op. cit.). 



28. Germ of a dipiionidian sp?cies. Hydrothecse partially developed (op, cit.). 



29. Germ of a similar species, fuller grown. Hydrothecse more developed (op.c.) . 



30. A fragment of the periderm of DiplograpsusWhitfieldi, showing a gonotheca, 

 or reproductive sac, from which two germs are just escaping (op. cit.). 



* All the figures marked a, and also Ic, 3c, 14c, 16d, 20, and 2G are natural 

 size. All marked b, and also 2c and d, 12c, 15c and d, and 17c, are enlarged 4 

 diameters. 2e, 21, and 27—29, are X 6 ; and 22 25, 12 diameters. 



