748 THE CRINOIDEA CAMERATA OF NORTH AMERICA. | 
Remarks. — The form under consideration was defined in 1883 by 
Willams as Arthroacantha, but the name was afterwards changed by Hinde 
to Hystricrinus, because it was, as he maintained, incorrectly formed, and 
a name too similar to Arthracanthus, previously employed by Schmarda ) 
for a genus of Rotatoria. We have formerly in Part III. of the Revision 
expressed the opinion that according to the rules of nomenclature Williams’ 
name would have to be retained, as it was sufficiently distinct from the 
other, even if changed to Arthracantha. The same view of the case was 
taken by Professor Whiteaves and Mr. 8. A. Miller, both accepting Williams’ - a 
name. If the question were to be decided by some authoritative body of | 
naturalists, we should vote in favor of suppressing Arthroacantha and legi- | 
timizing Hinde’s name, on the ground that no author should be permitted, i 
at this day, to establish a genus of Crinoids under any name which does not 
end with the recognized termination — “ crinus.” As it is, we have con- 
cluded, though with much reluctance, to retain the name proposed by 
Arthracantha is closely allied to Hexacrinus, from which it differs in having 
biserial arms, and movable spines upon the calyx and arms. The spines 
were probably attached to the plates by elastic ligaments, so as to yield 
when accidentally brought in contact with other objects; but we doubt if 
they represent either functionally or structurally the spines of the Echini. 
In this we differ from Williams, who thought that this structure establishes 
a relationship between Crinoids and Perischcechinoidea. He compares them 
with the spine-bearing plates of Lepidocentrus etfelianus Miiller, and is led to 
believe that these were probably plates in the “vault” of a true Crinoid 
like Arthracantha. We can see nothing to support this view; the Eifel 
species 1s undoubtedly an Hchinoid, and the plates of the two forms have 
a superficial resemblance, but are not homologous. The movable spines of 
Arthracantha, in our opinion, represent the sharp point of an ordinary spini- 
Williams, but writing it Arthracantha. 
f 
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ferous Crinoid plate, united with the basal portion by ligaments, and as 
the mobility of the spines of only generic importance, differing therein 
from Williams and Hinde, who were inclined to make Arthracantha the 
type of a distinct family. 
such are of but little importance in classification. We therefore consider | 
