HISTORY OF RESEARCH. xxvii 



Barraiule lias done in tlie case of Gr. prlodoa and (Ir. colonu.s.^' So anxions Avas 

 Scliarenljerg to avoid any confusion between normal and abnormal appearances, 

 that it led him into the opposite extreme of misinterpreting- several constant 

 specific characters, and attributing them either to the results of deformation or to 

 the special mode of preservation. 



4. Existence and Direction of Axis. — Scharenberg disagrees emphatically with 

 Barrande's view that the axis is never anything more than a single solid cylinder, 

 the sam? in a Diprion as in a Monoprion form. He explains the curious double and 

 vesicular appearance of the axis in some of the specimens of the D. pahneus as 

 figured by Barrande, by the theory that it not only represents the true axis itself, 

 but also a part of the common canal, from which the cells have been torn off before 

 fossilisation. In the case of Hhe two-branched forms, such as Gr. geminus, 

 Scharenberg points out that the axis must have divided or branched during life. 

 In all double (Iraptolites he thinks that the axis is invariably straight, while in 

 single-rowed ones it may assume almost any form. He does not consider that the 

 form of the polypary is constant in each species, except perhaps in the case of Gr. 

 turriculatus. 



5. The Texture of the Graptolite Stipe. — Scharenberg points out that this 

 character would be of the greatest importance in determining species if it could be 

 ascertained ; but, unfortunately, it can very rarely be observed. In the case of 

 Gladiolites, its peculiarities quite justify this form being made the type of a new 

 genus. He observes the horizontal grooves and markings (growth-lines) on the 

 cells in certain specimens of Grap)tolithns as " small thickened rings, like the 

 texture of many snail shells;" but, like Barrande, he does not suggest that they 

 are growth-lines. 



G. Niu)d>er of Cell Bows, and the Angle which the Cells make with the Axis. — 

 Scharenberg does not regard either of these characters as of much systematic impor- 

 tance. He holds that Barrande's separation of the Graptolites into Monoprion and 

 Diprion sections is also of little value, owing to the difficulty of determining in 

 scalariform views to which division a specimen belongs. 



7. The Inclination of the Cells to the Common Canal, and their Direction. — 

 These characters are of great moment, especially in those forms in which the cells 

 are in close contact. 



8. Tlie Distance of the Cells apart from each other. — This is also a reliable 

 method of distinction of species ; but Scharenberg does not agree with Barrande 

 that it is of generic value, as in the case of Bastrites. 



9. The Form of tlie Cells and their Apertures. — This is " undoubtedly the most 

 important criterion for the distinction of species." 



10. The Breadth of the Common Canal in Belation to the Length of the Cells. — 

 This is a character which deserves more attention than it has hitherto received. 



The most important })art of Scharenberg's paper is the general preface, dealing 



