——————— ee —— a 
BATOCRINID &. A487 
extremely long. First anal considerably longer than the radials, and much 
narrower at the upper end; it supports an elongate second anal, and at each 
side a large interbrachial; the succeeding plates are much smaller, and form 
a more or less protuberant area, which extends to the posterior oral, and 
contains the anus, which opens out laterally. Ventral disk conical or hemi- 
spherical, the interradial spaces somewhat depressed. Oral plates large and 
prominent; the posterior one larger than the other four, and central, either 
in contact with the latter, or separated from them by small perisomic plates. 
The food grooves covered by superimposed interambulacrals, and toward the 
margin of the tegmen by one or more large radial plates. Column long, 
composed of large and smaller pieces; the axial canal rather small and 
pentalobate. 
Distribution. — Known only from the Mississippi Valley, where it occurs 
in both Burlington beds, and also in the Keokuk group. 
Type of the genus: Agaricocrinus americanus. 
Remarks. — This genus is most remarkable for the depression of the 
dorsal cup, of which in the typical form only the arm facets and portions 
of the interbrachials can be seen in a side view, the lower parts being flat or 
more or less concave. Another good character is furnished by the distichals, 
which, taking the form of arm plates, curve inward and interlock with one 
another; and last but not least, by the ponderous, gradually tapering, 
biserial arms, and the elongate form of the interbrachials. In all of these 
Agaricocrinus differs essentially from Aorecrinus and Dorycrinus, with which 
it has certain affinities. It has been most frequently confounded with 
Amphoracrinus, to which in some species it has a superficial resemblance in 
the form of the calyx; but the arm structure and position of the anus in the 
two genera are different, and, in the typical forms, Amphoracrinus has only 
two plates in the row above the anal plate. For specific separation we 
rely upon the variations in the proportions of the interbrachial plates, and 
the form and size of the costals and distichals, as the best distinctive char- 
acters. The number and distribution of the arms, the form of the anal area, 
and the condition of the oral plates, are also important. 
