Wachsmuth and Springer—Silurian Orinoids. 267 
Mr. Miller considers it probable that Gi. Harrisi has five 
basals, because “in ther respects it agrees with Glypto- 
crinus”—not recognizing the difference in the disposition of the 
anal plates—but states that “if it possesses but four, it would 
not belong to Xenocrinus, but would still be very closely allied 
to Glyptocrinus.” We confess we are somewhat at a loss to 
understand just what Miller’s views are, as to the limits of this 
Sere eee 
Species to Feteocrinus, and at one place considers the 
O’ Nealdi and his own Gl. cognatus, and therefore necessarily GZ 
ri, to be true Glyptoc . At another, in describing his 
Gl. Patersoni (Journ. Cin. Soc., July, 1882), he states that the 
O'Nealli and Gi. Beri, but also Gl. cognatus which he had 
himself described a year previously, have but ten arms; but 
we infer that he then considered these species to be generically 
distinct from Glyptocriuus. If this be not so, how can it be 
said that Xenocrinus priscillus, which is in every respect a Gi. 
with four basals and a oe column, would be generi- 
eveloped, They 
are among the earliest forms we know, and they stand in a 
similar relation to these families that Heterocrinus and its allies 
hold to’ the Cyathocrinidx. In both there is the same rudi- 
mentary and varying development of characters, which when 
xed and constant, become of family importance. In both are 
found the types of the fundamental structure of the respec- 
tive families in very simple forms, whose differentiations in 
various directions led to the several subdivisions and genera, 
into which these families have been divided. ithin each 
there is found a commingling of characters which is a source 
of endless perplexity to those who are seeking to discover some 
clew to a natural classification. We are disposed to think that 
a further subdivision of the families, whereby these embryonic 
types should be placed in separate subfamily groups, would 
tend to eliminate some of the Vificulties we have encountered, 
