1868.] NicnoLsox — coniston-flao graptolites. 529 



mode of preservation, the direction in which compression has been 

 effected, and the particular view which is afforded by any given 

 specimen. 



When compressed from side to side, or at right angles to the cel- 

 lules, the cell-mouths appear as quadrangular or oblong notches, 

 rounded at the base, and extending into the body of the stipe, tho 

 external terminations of the apertures being on a level with tho 

 outer margins of the frond. About 30 of these notches occupy the 

 space of an inch. This form is the one which was described by 

 Prof. M'Coy under the name of Diplograpsus rectangularis. When 

 compressed from back to front, the cell-mouths appear as oval-oblong, 

 sometimes linear, sometimes lunate, apertures, at right angles to the 

 direction of the frond, and about 30 in the space of an inch. Ac- 

 cording as the compression has been directly from back to front, or 

 according as more or less of the lateral surface is exhibited, will the 

 apertures of one or both rows of cellules be partially or entirely dis- 

 played, the variations in this respect being numerous. 



When preserved in the round, and viewed from side to side, the 

 septum between the two simple stipes which together form the frond 

 exhibits its lateral margin as an " impressed median line, which is 

 generally straight, but is sometimes a little wavy between the cells " 

 (Salter). The variations in this species are so numerous, its struc- 

 ture is so remarkable and withal so readily interpreted, and it throws 

 so much light upon the nature of Graptolites in general, that I shall 

 content myself for the present with the above brief description, re- 

 serving a more detailed account for a paper which I am preparing 

 upon the British species of Diplograpsus and Climacograpsus. There 

 are, however, two abnormal appearances which I may notice here, 

 as they are exhibited by specimens which I have obtained from the 

 Coniston Flags. The first of these consists in the attachment to 

 the proximal extension of the solid axis of several small, apparently 

 vesicular bodies which occur on both sides of the axis, and are also 

 attached to the margins of the frond itself near the base. The 

 second consists in the occurrence of a form of Diplograpsus display- 

 ing plain margins, with a filiform central axis, and with no indica- 

 tion of cell- apertures beyond a slight crenation of the margins. 

 These specimens, at first sight very puzzling, I have determined to 

 be really GUmacograpsus teretiusculus split in half, so as to present 

 to view nothing but the vertical septum which divides the frond, 

 and along the centre of which the axis runs. The correctness of 

 this view is established by the examination of a specimen shown, 

 partially in relief and partially as an impression, the former portion 

 exhibiting the characters above mentioned, whilst the latter displays 

 transverse cell-apertures. 



Log. Yery common, and beautifully preserved in relief in the 

 Coniston Flags of Skelgill Beck, near Ambleside ; also, as impres' 

 sions only, in the flags of Mosedale in Long Sleddale. 



Genus Ketiolites, Barr. 

 Frond diprionidian, linear, with subparallel margins. The cel« 



2o2 



