ORDER IIT CRINOIDEA—FISTULATA 155 
Family 7. Gasterocomidae. Wachsmuth and Springer. 
Base dicyclic. Infrabasals anchylosed into an undivided disk, which is pierced 
by a large quadrilobate canal. Radials large; articular facets directed outward, 
horseshoe-shaped, occupying nearly the whole outer face of the plates, and pierced by a 
large dorsal canal. Anal opening low down, situated directly above the anal plate and 
between two radials. Tegmen composed of five interradials, five orals, and ambulacral 
plates. Devonian. 
Gasterocoma, (Goldf. (Epactocrinus, Miller), (Fig. 257). Infrabasal disk 
extending but slightly beyond the column; surrounded by five B, of which 
the posterior one is slightly truncated. 
ft five, three of them equal, the two 
posterior ones irregular; the latter 
enclose the JA and anal opening, 
which is surrounded by a few small 
pieces. The arms, as indicated by the 
character of the radial facets, either 

recumbent or widely divergent. De- Fic. 257. 
yonlan ; Eifel. Gasterocoma antiqua, Goldf. Devonian ; Priim, 
Sis lens 2 as Eifel. a, Calyx seen from one side; b, Anal aspect; 
Nanocrinus, Miller. Similar tothe  ¢'Teamen. 2); (after TBEReo ie SL 
preceding, but only four of the R 
arm-bearing. The right antero-lateral one, however, has two articular 
facets, and evidently supported a pair of arms instead of a single one; the 
anterior £ is considerably smaller, and has no articular facet. Devonian. 
Achradocrinus, Schultze ; Scoliocrinus, Jaekel. Devonian ; Germany. 
Family 8. Cyathocrinidae. Roemer (emend. Wachsmuth and Springer.) 
Base dicyclic. Radials simple or compound; their upper edges furnished with 
a small crescent-shaped facet. Radials and arm-plates united by close suture, as are 
the latter among each other. IRA usually, and RA occasionally present.  Tegmen 
with fie orals and a madreporite, extended into a strong ventral tube. The disk: 
ambulacra resting on the lateral margins of two large interradial plates; they are 
lined by side-pieces, and roofed over with covering plates. Arms without pinnules, 
long, branching, and uniserial. Ordovician to Carboniferous. 
Dendrocrinus, Hall (? Palaeocrinus, Billings). Calyx obconical, higher than 
wide, unsymmetrical. Jb five, equal. JB five, the largest plates in the 
calyx; the posterior one truncated at its upper face, and supporting a large 
anal plate. Four of the & pentagonal and simple; the right posterior one 
compound, with the two parts vertically arranged. JRA succeeded by two 
or three plates which form the base of the ventral -sac, but are partly 
enclosed in the calyx. Ventral sac very large. Arms long and branching ; 
column sharply pentagonal, or sub-pentangular. A number of species occur 
in the Ordovician of North America, but only a single doubtful one known 
from the Silurian (Niagara Group). 
Homocrinus, Hall (Fig. 258). Like the preceding, except that the arm- 
bearing portion of the right posterior radial is pushed over toward the right, 
so as to support, conjointly with the anal, the ventral sac. Silurian; North 
America. Devonian; Rhineland. 
Gastrocrinus and Rhadinocrinus, Jaekel ; Bactrocrinus, Stein. Devonian. 
