64 PROCEEDINGS OF THE GEOLOGICAL SOCIETi". [Mav 16, 



Graptolites coxYOLrTrs, Hisbiger. 



In some specimens, probably voung, the axis is Terr narrow com- 

 pared to the length of the serrations, being httle more than a mere 

 Ime. In other specimens the axis becomes broader and shows a de- 

 pressed line along the middle. This relative thickening and increase 

 of the axis with age has already been noticed bv Geinitz*. In some, 

 perhaps very old varieties of this species, the axis is much less curved, 

 and the serratm-es much shorter. They form merely a series of very 

 obtuse and wide teeth, scarcely projecting beyond the margin. This 

 may foim a distinct species: but thevariarions evidentlv produced by 

 age, or from the manner of imbedding in the stone, as seen in differ- 

 ent parts of the same specimen, show that much caution is required 

 in such distinctions. 



Graptolites ludexsis, Murchison. 



The specimens agree very well with the figure given in the 'Silurian 

 Systemf.' The most important difference is in the more rounded, 

 almost club-shaped form of the ends of the serratures in the fossils 

 from Peebies-shire. This probably arises from the specimens being 

 in a more perfect state of preservation. In some of the larger speci- 

 mens both of this species and of the G. SednuAcMi, Portlock, the 

 stem near the root is nan-ow and almost destitute of serratures, but 

 becomes broader and the seiTatures very distinct as it ascends. 

 Where also the back of the specimen only is exposed, the serratures 

 may be wholly concealed, so that it appears entu'ely destitute of these 

 appendages, and such a fragment might readily be taken for a new 

 species. TVhere the opposite side again is turned to the spectator 

 the serratures are pressed flat, and appear hke broad lobes divided by 

 narrow depressions, giving tbe stalk a jointed appearance. TVhere 

 the back is well-seen, it is marked by a fine gi'oove run n ing along its 

 centre. Some of our specimens are fiom 10 to 12 inches long, though 

 imperfect at both ends. 



Graptolites laxus. 



The fohaceous species fr'om Thornielee, mentioned above, some- 

 what resembles the G. pristis, Hisinger, but the axis is much nar- 

 rower, and the serratures louger in proponion to then- breadth (or 

 length to breadth rather more than 2:1). They are also separated 

 by an interval equal to then* own width, or even more, a character not 

 seen in any other fohaceous species figured. In this respect it differs 

 so much from the general aspect of the genus, and so closely resem- 

 bles some plants of the moss-tribe {Hypium), as to render its real 

 character doubtful. If a true graptohte, it seems undoubtedly a new 



* Leonliard and Bronn's JatLrbuchfiir 1S42, p. 701. The G. spiralis of Geinitz 

 seems identical with the G. co/ivolufus, Hisinger. 



t Plate 26, figs. 1 and la. In this work the importance of these fossils, as 

 distinguishing diiierent parts of the Silurian formations, was first made known to 

 geologists. See pp. 206, 694. 



