64 
SMITHSONIAN INSTITUTION 
Order FLEXIBILIA Zittel 
CrINOIDS with a flexible calyx in which the lower BRACHIALS are LOOSELY! INCOR- 
PORATED INTO THE DORSAL CUP EITHER BY LATERIAL UNION WITH PIACH OTHER, BY MEANS 
OF INTERBRACHIALS, OR OF A LOOSE SKIN STUDDED WITH CALCAREOUS PARTICLES. AlL 
PLATES BEYOND THE RADIALS UNITED BY LOOSE SUTURE, AND MORE OR LESS MOVABLE. 
Mouth and tegminal food grooves exposed. Base dicyclic, with three infra- 
BASALS, UNEQUAL. ArMS NON-PINNULATE. StEM ROUND. 
In view of the fact that this order of the Crinoidea has recently been treated mono- 
graphically in my work on the Crinoidea Flexibiha, 2 volumes 4to, Smithsonian Publication 
2501, 1920, in which nearly all the species occurring in the areas here under consideration 
have been fully described and their generic relations discussed, it is not deemed necessary to 
repeat the descriptions, or to do more than give a list of the genera and species with references 
to that work where the complete bibliography will be found, together with a selection of the 
principal figures — for the greater convenience of students of the Silurian faunas. 
Of the Flexibiha group there have been recognized from this area 10 genera and 18 
species, all but two of the genera from Tennessee. Three of the species are new; ii are from 
Tennessee, 6 from Indiana, and one from Ohio. They are distributed among the four fami- 
lies of the order as follows: Lecanocrinidae 12, Sagenocrinidae 2, Tchthyocrinidae 2, Taxo- 
crinidae 2. Thus the great preponderance of this type as found in the present collections be- 
longs to the small, robust and better preserved Lecanocrinidae. 
Of the ten genera, nine are common to both Europe and America. Of these, six were 
formerly considered to be exclusively Swedish and English. One newly described genus is 
represented by species from both continents. One highly typical Gotlandian and English 
genus, Pycnosacais, hitherto barely recognized in this country, appeared in the Beech River 
formation in considerable abundance, one species of which can scarcely be distinguished from 
its foreign prototype. Sagenocrinus, another specialized form of the European Silurian, is 
represented here by a thoroughly typical species. And a third, Gnorimocrinus, now appears 
for the first time in America. Besides these important contributions from the Tennessee 
Silurian there are two well defined new genera, Hormocriniis and AsapJiocrinus, in the form 
of finely preserved specimens, the first of which also occurs in Europe as new species. Thus 
the Elexibilia, usually the rarest of the crinoids, take their place among this fauna as one of 
its most important constituents. 
SuLwder SAGENOCRINOIDEA 
Posterior iiiterradiiis either not differentiated or containing- anal plates, 
not usually formed into a tube, the first of which is incorporated in the calyx 
by sutural union with adjacent brachials for at least part of its height on both 
sides; posterior basal, if difl'erentiated, truncate or angular, and suturally con- 
nected with succeeding- anal plate. 
Family LECANOCRINIDAE Springer 
Infrabasals more or less erect, forming an essential part of the calyx wall ; 
crown usually short, rotund. 
