GRAPTOLITES OF NEW YORK, PART 2 4 1 I 



fact that the thecae are not growing exactly in the axial plane of the com- 

 mon canal, but are all slightly curving out of this plane toward the obverse 

 side, which thereby becomes flat or concave in section, while the reverse 

 side from which the thecae grow away, becomes depressed towards the 

 margins and convex in section. Hall's original section (6) shows this 

 position of the thecae very well. 



This is not the only peculiar character of this species, distinguishing it 

 from nearly all of its congeners in this country. The narrow spikelike sicu- 

 lar part with its widely separated thecae is another feature not observed in 

 other species and the absence or very late separation into two series of 

 thecae and the correlative late formation of a dividing septum constitutes a 

 third distinguishing character. 



The mature parts of C . latus Elles and Wood, a form of the last 

 Champlainic (Ordovicic) zone in Europe, resemble those of this species 

 very much in the broad lateral face and relatively small squarish free parts 

 of the thecae. We undoubtedly have to see in it a vicarious form of the 

 late Champlainic derivatives of C. typical is described in this memoir. 



Climacograptus typicalis Hall mut. spinifer nov. 



Plate 28, figures 8, 9 



Inspection of the original of the first figure of C. bi corn is illus- 

 trating Hall's description of that species shows at once that this specimen, 

 which comes from Ballston, Saratoga co., differs greatly from the typical 

 C . bicornis, as it occurs in the Normanskill shale. We reproduce here 

 a more exact drawing [pi. 28, fig. 8] of the same to bring out its peculiar 

 characters. The State Museum contains slabs from Bakers falls in the 

 same county, which are identical in their lithologic characters with the 

 slab bearing Hall's original and like that slab contain no other fossils but 

 this graptolite, that proves to be a peculiar mutation (or variation ?) of C . 

 typicalis. The character of the earliest thecae [see text fig. 363] is 

 especially convincing of this. The rhabdosome remains, however, distinctly 

 narrower (in Hall's original its width is only 1.2 mm, in the widest speci- 

 mens from Bakers falls 1.8 mm) and the thecae are closer arranged, the 



