730 ME. J. E. MAEE AN^D DE. H. A. K^ICHOLSON 



EXPLANATION OF PLATE XVI. 



Unless otherwise stated, the figures are of the natural size. 



Fig. 1. Fhacops elegans, Boeck & Sars : internal cast of glabella, Glaber-zone, 

 Skelgill, X 2. 

 1 a. Ditto : a small tail, X 2. 



2. Ditto : from a wax impression of intaglio of head and anterior bodj^- 



rings, Erinaceiis-zone, Torver Beck. 



3. Ditto : internal cast of a nearly complete specimen, Glaber-zone, Skelgill. 

 3 a. Ditto : glabella and cheek of the same specimen, from a wax impres- 

 sion of internal cast. 



35. Ditto : diagrammatic sketch of incurved lower margin of cheek of the 

 same specimen, showing cavities for the reception of the extremities 

 of the pleurse, X 4. 



4. Ditto, yar. nov. glaber : internal cast of tail, Glaber-zone, SkelgilL 



5. Pkacops mucronatus, Brong. : internal cast of glabella, Aloniensis-zone, 



Browgill. 



6. Ditto : tail from same zone and locality. 



7. Cheirurus bimucronatus, var. nov. acanthodes : glabella and cheek, 



Glaber-zone, Skelgill, X 2. 



8. Ditto : tail, restored, from a second specimen, same zone and locality. 



9. Cheirurus moroides, n. sp. : from a wax impression of an external mould 



of the glabella, Glaber-zone, Skelgill, X 2. 



10. Ditto: from a wax impression of an external mould of the glabella, 



Glaber-zone, Skelgill. 

 10 a. Ditto : details of ornamentation of the samej highly magnified. 



11. Acidaspis erinaceus, n. sp. : Erinaceus-zone, Torver Beck, X 2, 



12. Ditto : a younger specimen, same zone and locality, X 2. 



13. Harpes judex, n. sp. : slightly distorted, the wrinkles on the centre of 



the glabella being apparently due to this, Aloniensis-zone, Skelgill. 



14. Ditto : a crushed head, showing the venose structure, Glaber-zone, 



Skelgill. 

 14 a. Ditto : a portion of the same specimen, highly magnified. 



15. Harpes angustus, n. sp. : head, and cast of portion of body, Aloniensis- 



zone, Skelgill, X 2. 



16. Ditto ; internal mould of head, Glaber-zone, Skelgill. 



16 a. Ditto : a portion of the same, highly magnified, showing punctations. 



17. Ampyx alo7iiensis, n. sp. : from a wax impression of intaglio, Aloniensis- 



zone, Skelgill, X 3. 



18. Proetiis brachypygus, n. sp. ; from a wax impression of intagho, Alo- 



niensis-zone, SkelgiU, X 2. 



19. Ditto : Aloniensis-zone, PuU Beck, X 2. 



20. Atrypa fiexuosa, n. sp. : ventral valve, Flexuosa-zone, Skelgill. 

 20 a. Ditto : the same S]Decimen, dorsal valve. 



20 b. Ditto : ditto, anterior view. 



Note. — In fig. 2 the axis should be extended through the lowest (imperfect) 

 body-ring. In fig. 19 the glabella-lobes are made too wide. 



DlSCFSSION. 



The Peesideistt observed that the more minute details of strati- 

 graphical geology were as important as divisions of wider range, 

 especially in the Palaeozoic rocks. He referred in illustration to 

 the work done in Bohemia by one of the Authors. 



Prof. Lapwoeth looked forward to the day when the existence of 

 these Graptolite-zones in Lower Palaeozoic rocks would be generally 

 acknowledged, and they would be employed as a basis for classifi- 



