1 92 NEW YORK STATE MUSEUM 



feature in that "one side of the branches is furnished with prominent spines 

 or denticles, which appear to mark the cell apertures," and compares it with 

 Dendrograptus, stating as difference, that it is stronger and more bushy 

 than species of that genus, and has conspicuous spines indicating a different 

 cell structure. 



Lapworth has later [1881] asserted its presence in Wales and Scotland, 

 and suggested that Acanthograptus, if the denticles are horizontal, will be 

 found to lie somewhere near Thamnograptus. Since these conclusions are 

 based on Spencer's insufficient diagnosis it is quite possible that the British 

 forms belong elsewhere. 



Gurley adds in his manuscript to Spencer's diagnosis : 



This is apparently a good genus, including several species which present 

 a very similar fades, principally in the plumulose branches with a tendency 

 to a 2 — or 3 — spicate termination. But if this genus be altogether distinct 

 from Inocaulis (a point on which at present I do not feel positive), it is 

 certainly here that Spencer's Inocaulis walkeri belongs. 



The type of this group is A. grant i, the first of the species 

 described. The latter and several other hitherto undescribed species from 

 Hamilton, present the extreme development not in numbers but in size of 

 the "spines," and for this reason present an aspect quite different from that 

 of I . p 1 u m u 1 o s u s \_see pi. 6, fig. 3, representing a fine specimen loaned 

 to us by its collector, Mr Schuler in Rochester), but identical with that of 

 Inocaulis suecica and I. musciformis YViman. Since we have 

 also observed in Canadian species of Acanthograptus a like composition of 

 the spines of several emptying tubes [see pi. 7, fig. 4| as has been found in 

 the Swedish, we can safely cite here the results of YViman's important 

 observations | sec text fig. 94-96]. 



In A. suecicus which is the better known of the two species 

 Wiman observed that the branches bear the- branchlets which proceed alter- 

 natingly to the right and left in pennate fashion and consist each of four 

 successively opening individuals. Only two of these are visible on figure 

 95, the other two opening on the reverse side ol the branchlets. These 

 four individuals belong: to four different gfenerations and they consist of two 



