164 BULLETIN OF WISCONSIN NATURAL HISTORY SOCIETY. VOL. 4, NO. 4. 
of a fine original stellation. One or two spines, instead of having 
the anterior margin uniformly curved, show a slight angulation 
at the region of maximum width, in that the spine tapers grad- 
ually from this point in both directions, distally and proximally. 
Obviously these spines, differing as markedly as they do from 
the majority of Palaeozoic ichthyodorulites, cannot be included 
under any known genus or species. We therefore propose the 
new genus Phlyctcenacanthus for their reception, and have pleas- 
ure in naming the species P. telleri, * * *. 
Regarding their affinities, we can only suggest that they may 
have pertained to ■ Palceomylus. Their large size precludes an 
association with either Rhynchodus or Ptyctodus; and Ciadodus, 
the only other Elasmobranch known to occur in the Wisconsin 
Hamilton, was in all probability a spineless shark. On the sup- 
position that they were the spines of Ptyctodus ferox, then we 
ought by good rights to have found similar fossils in the Slate 
Quarry fish beds, where there is such a wonderful concentration 
of Ptyctodus remains. But such spines as have been recovered 
from the Iowa locality are very different from Phlyctcenacanthus, 
The latter are thus definitely excluded from all known genera 
occurring at Milwaukee, except Palceomylus. But as we know 
nothing, for instance, of the denition with which Heter acanthus 
politus was associated, so, too, there is as much likelihood of 
P. telleri belonging to some unknown Elasmobranch genus as to 
Palceomylus. But as to the relative probability of one of these 
"genera" of Milwaukee ichthyodorulites belonging to the Ptycto- 
dontidw, the evidence of the tuberculated Russian fin-spines would 
go to show that Phlyctcenacanthus is the likelier of the two to have 
its position established here. * * *." 
At the time of the writing of that article, but few specimens 
of the species had been collected, the best one of them being used 
as the type of the genus and species as described. Since then a 
few more specimens having been secured that throw more light 
on its structure, it has been thought proper to reprint that portion 
of the original description with such other information as we now 
have from the new material at hand. The difficulty of obtaining 
anything like perfect specimens at the locality can only be appre- 
ciated by those who have collected these, and while the nature of 
the formation is such as to give the impression that they should 
