158 ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
Streptocrinus, W. and Sp. (Ophiocrinus, Ang. non Salter nec Semper). 
Plates of the dorsal cup as in Cyathocrinus. Ventral sac composed of about 
eight rows of hexagonal plates, some of which are deeply folded transversely, 
so as to produce well-marked depressions on the surface. Arms slightly 
bending downward; their ambulacral grooves narrow, and provided with 
covering pieces only. Silurian ; Gottland. 
Tenarocrinus, Bather. Dorsal cup broad, and composed of thin plates ; the 
truncated posterior B supporting a large Jd. The right posterior & com- 
pound; its superradial shifted to the right; but the inferradial, notwith- 
standing its slanting position, gives no support to the ventral sac. The latter 
is very large, longitudinally folded, and covered with transverse rows of 
pits. Column round, with very wide axial canal. Silurian; Dudley, 
England. 
Parisocrinus, W. and Sp. Dorsal cup obconical, composed of five LB, five 
B, and five f, with an anal and radianal; the latter two together supporting 
the long, cylindrical, ventral sac. Upper edges of the / excavated so as to 
form a narrow semicircular facet for the reception of the first costals ; 
number of the latter very variable among the rays. Arms multibrachiate, 
divergent, and filiform at their tips. Column round. Devonian ; Germany. 
Sub-Carboniferous ; North America. 
Atelestocrinus, W. and Sp. Dorsal cup elongate, always more or less con- 
stricted along the suture line between the basals and infrabasals. JB five, 
large, forming an almost solid ovo-cylindrical body. 4 five, long and narrow ; 
FR five; four of them equal and arm-bearing, the anterior one less than half 
the size of the others and not arm-bearing. Costals 4 x 4, the uppermost 
axillary, and supporting two main arms; armlets given off on alternate sides 
from every second plate. Anal interradius as in the preceding. Burlington 
and Keokuk Groups; Mississippi Valley. 
Sphacrocrinus, Roemer, and Achradocrinus, Schultze. Of these only the 
structure of the calyx is known. ‘The dorsal cup in both forms is globular, 
composed of very thin plates, and the arms are pierced by a dorsal canal. In 
the first-named genus Jd and LA are both represented, and it has an 
eccentric anal opening which is directed upwards. But in the second fd is 
wanting, and the position of the anus is strictly lateral, it being situated in 
the suture line between the posterior radials. Middle Devonian ; Eifel. 
Codiacrinus, Schultze. Calyx small, resembling a poppy head. JB five ; 
B five; R five; the plates within each circlet equal to one another, and 
laterally in contact. Devonian; Germany. 
Lecythiocrinus, White. Arrangement of calyx plates as in the preceding, 
but with wider radial facets ; these are directed upwards instead of obliquely 
outwards, and are provided with transverse ridges and well-defined ligamentous 
fossae. Coal Measures; North America. 
Family 9. Poteriocrinidae. Roemer. 
Base dicyclic. Infrabasals five, sometimes hidden by the column.  Basals fire ; 
radials five, with transverse articular ridges. Anal and radianal generally repre- 
sented ; and lower plates of the tube frequently entering into the dorsal cup. Ventral 
sac large; elongate or balloon-shaped in the earlier forms, small and conical in the 
later ones ; it is composed of hexagonal plates, having the angles perforated by pores. 
