xiv BRITISH GRAPTOLITES. 



1849. In tlie same year Hall discussed the geological range of the 



Hall Graptolites in America in some detail. He observes that 



" On Graptolites : tlieir they are peculiarly typical of the Lower Silurian ; " few are 

 Duration in <^^^_l^gj^^^^ known in a higher position, being less widely distributed and 

 in the IdentificTtion of ^^^7 limited in geological range." That is to say, there are 

 Strata," ' Proc. Amer. fifteen species found in the Lower Silurian, and three in the 

 Ass. for the Advance- Upper Silurian. Of these three species, two — Gr. clintonensis 

 meut of Science.' g^^j Qy^ vGnosus — are peculiar to America, and occur towards 



the base of the upper division in the Clinton group, and the third — Or. Indensis — 

 at a slightly higher horizon. 



He describes the new form Gr. venosus (which is now known to be a 

 species of Barrande's genus lietiolites) as " broad, with a central capillary 

 axis and serratures on both sides." The whole substance is finely veined or 

 reticulated, like the skeleton of a leaf. On account of its peculiar structure 

 he thinks it may " very well form the type of a new genus in the future." Hall 

 does not discuss the affinities of Graptolites fully, but as it is impossible to trace 

 the connection of these fossils with any living forms through the Devonian and 

 Carboniferous rocks, he is " disposed to question their analogy with the Sertu- 

 laridge or PennatulidEe." 



In 1850 M'Coy gave a diagnosis of the family of the 

 ,,' ■ Graptolitid^B in the following words: — "Stem simple or 



M'Coy, ^ or 



" On some New Genera hi'^nched, thin, usually linear, horny, unrooted ; polyp cells 



and Species of Silurian divided at bottom by a transverse diaphragm." M'Coy was 



Eadiata in the Collec- thus the first palaeontologist to draw attention to the " free " 



tion of the University nature of the Graptolites, and he points out distinctly that in 



1' this particular they differ from the Sertularidae, "with which, 



' Ann. Mag. of Nat. ^ '' . 



Hist. ' ser. 2 vol. vi. however, they agree in the form of the polypidom and the 



cells." His view of the presence of a transverse diaphragm 



at the base of the cells was probably obtained from an examination of Lake 



District specimens, as markings suggestive of septa were described later by 



Hopkinson from similar material. 



As regards the method of reproduction of the Graptolites, M'Coy acknowledges 

 that no ovarian vesicles have been found so far, but he suggests that the ova were 

 developed in naked sacs attached to the base of the tentacles of the polyps, and 

 hence were not preserved : this position of the reproductive organs would be 

 analogous to that in Corymorplia. His views, he is careful to point out, are much 

 the same as those previously published by Nilsson and Portlock. 



An important advance as respects the classification of the Graptolites was made 

 by M'Coy in this paper, for he recognises that the structural differences between 

 the uniserial and biserial forms ought to be regarded as of generic value, 

 and suggests that the name Graftolites should be restricted to the former 



