A Neiv Cystocrinoidean Species. — Sardeson. 271 
genera with an anal plate where the form of the basal disc 
is changed from pentagonal to hexagonal, as a bisection of 
the larger plates would produce six plates instead of five." 
It is necessary for them to explain away the apparent sixth ele- 
ment which they do by ascribing increased width of one plate 
coinciding with the intercalation of the anal plate. The azy- 
gous plates are not considered as primitive, according to 
that view. 
Strophocrinus shows on the contrary that the sixth infra- 
basal element should be interpreted as an anchylosed plate, 
where it is evident, and a comparison of Crinoidea to cysto- 
crinoidean types will show that no azygous or anal plates need 
be viewed as intercalated. Comparison of primitive Cystoidea. 
with cystocrinoidean types and Crinoidea, shows an evident 
reduction in number of plates in the abactinal side of the calyx, 
and further reduction characterizes later crinoidean develop- 
ment. No other explanation for the asymmetry and the azy- 
gous plates in Strophocrinus is needed, as it seems, than that 
the change from the hexamerally distributed arrangement of 
plates in certain cystids to that of pentameral arrangement and 
reduced number of crinoidean plates is imperfectly accom- 
plished. From this view point, Strophocrinus appears nearer 
the true transitional type from Cystoidea to Crinoidea than 
either Cariocrinus or Porocrinus does, both of which are too 
far advanced in the reduction of infrabasals to represent the 
ancestral type of such crinoidea as Carabocrinus. Cariocrinus 
has four infrabasals, equivalent in dimension to six, i. e., the 
circle of four build an hexagonal area. Porocrinus has five, 
equivalent to five. Strophocrinus has five, equivalent to six, 
as Carabocrinus also has. Crinoidea of course more often 
have the equivalent of five. The basals also are only five in 
Porocrinus, although six in Cariocrinus, six in Strophocrinus 
and Carabocrinus, five in most Crinoidea — always five in these, 
in fact, if a certain plate be called not a basal. Porocrinus 
has but one azygous plate, Cariocrinus has the equivalent of 
several, Strophocrinus has four or five, Carabocrinus has three, 
and Cyathocrinidse generally have two or one, i. e., a radianal 
and an anal plate. 
If we represent the cystocrinoidean composite type as an- 
cestral also to Crinoidea, i. e., six infrabasals, six basals, and 
