

Graptolites. 373 



form. Besides, we find this very variable amongst the grap- 

 tolites themselves. Nor is the fact that the poiyparies were 

 free of mnch significance, inasmuch as there are free forms 

 among both the Polyzoa and Hydrozoa. The only trustworthy 

 characters for the purpose we want are to be obtained, I 

 believe, from the structure and relation of the individual parts 

 of the polypary. In the Polyzoa there is a distinct septuni 

 cutting off the individual from the common canal, except by a 

 comparatively small perforation. In the Hydrozoa the polype 

 rises directly from the ccenosarc, and this also is the structure 

 of the graptolite. This would, then, at once set aside the 

 Polyzoa, and restrict the inquiry to the humbler ccelenterate 

 zoophytes. The general resemblance between the free Pen- 

 natula, with its prolonged axis and bilateral arrangement of 

 parts, and Diplograpsus, will not bear even a little scrutiny. The 

 axis is slender and corneous, and is produced at the distal end 

 of the organism, while in Pennatula it is thick and fleshy, and 

 proceeds from the proximal end. The cells containing the 

 animals are dug out of the ccenosarc, and strengthened with 

 calcareous deposits in Pennatula, while in the graptolites the 

 polypary is corneous and external, agreeing in this respect 

 also with the Hydrozoa. There are, no doubt, some struc- 

 tures for which it is difficult to find anything corresponding 

 among the Hydrozoa ; but making every allowance for them, 

 and considering the many and important points which they 

 have in common, there is a strong case made out for the 

 graptolites being Hydrozoa, although a somewhat abnormal 

 form. 



EXPLANATION OP PLATE II. 



Fig. 1. GraptoUthus Sedgwickii, Portl. 



Fig. 3. GraptoUthus Hisingeri, Car. a, portion of the 

 adult polypary ; c, proximal end, with small cells ; b, young 

 specimen of an allied species. 



Fig. 7. GraptoUthus Haiti, Barr. 



Fig. 8. Two perfect specimens of GraptoUthus Cling ani, Car. 



Fig. 15. Fragments of GraptoUthus convolutus, His. 



Fig. 2. Diplograpsus pristis, His. sp. a, complete poly- 

 pary ; b and c, different forms of the proximal spines. 



Fig. 4. Diplograpsus cometa, Gein. Three' different forms. 



Fig. 5. Diplograpsus folium, His. sp. a, complete poly- 

 pary ; b, portion magnified ; c and d, young individuals. 



Fig. 6. Climacograptus scala?°is, Linn. sp. 



Fig. 9. Rastrites Linnaii, Barr. 



Fig. 10. Past rites capillaris, Car. 



Fig. 11. Didrograpsus aranea, Salt. 



Fig. 12. Dldijuwgrapsus Murchisonii, Beck. 



