272 The America7i Geologist. November, 1899 
about ten radials, including azygous plates, then Stropho- 
crinus stands intermediate to that type and Carabocrinus and 
other Cyathocrinidse, and it thus indicates what direction a line 
of evolutionary development may have followed between Cys- 
toidea and Crinoidea. This suggested relationship harmonizes 
the conspicuous long since recognized (Hall, 1852) relation 
of the four infrabasals of Cariocrinusornatus Say., to six hypo- 
thetical equal elements, as also the relation of five infrabasals 
to six elements in Strophocrinus, Carabocrinus, et al. It har- 
monizes the six symmetrical basals found in Cariocrinus and 
in Strophocrinus and the same as represented in Carabocrinus. 
The "radianal," the anal and other posterior azygous plates of 
the Order Fistulata, as well as the azygous plates in Porocri- 
nus, compare readily to the less reduced structure in Stropho- 
crinus. Even the "supplementary radial" plates of monocyclic 
Fistulata, which, as we are told, are of great taxonomic im- 
portance, might in like manner be compared to the basals, 
])arabasalia,of such a form as Strophocrinus; and in the absence 
of any evident rudimentary infrabasals in forms closest related 
to Bserocrinus and Hybocrinus, and in view of the supplemen- 
tary plates in these being in the position of basals, as seen in 
Strophocrinus, one might not perhaps be criticised for sug- 
gesting that two lines lead from dicyclic to monocyclic forms, 
tlie earlier one through reduction of basals, the later one 
through reduction of infrabasals. In the former the paraba- 
Falia fuse with the radials, in the latter the infrabasalia fuse 
together and form the top of the column. 
It nia\' be further noted that pentameral crinoidean sym- 
metr\' is least, probabl)- also last, developed in the circle of 
radials, or the equatorial zone of the cah'x. Pentameral 
symmetr}' seems to have developed from the stalk upwards 
and from the apex or mouth outwards. Among Cystoidea 
two, three, four, five and six ambulacral furrows appear, the 
number being inconstant in some cases. In Strophocrinus 
the pentameral S3anmetry of the stalk and of the ambula- 
cra seems much like a coincidence with not yet far develop- 
ed consequences as to the patina. Even the symmetry of 
the five arms as far as known is incomplete, the posterior 
pair being smallest. 
