ACTINOCRINUS SENECTUS, 11. Sp. 



Plate II, Fig. 23, azygous side; Fig. 24, opposite view; Fig. 25, 



summit. 



Species medium size. Calyx obpyramidal, truncated only the 

 diameter of the column, transverse section subpentagonal. Radial 

 ridges sharply angular, interradial plates convex. Diameter about 

 one fourth more than the height, column round. 



Basals form a round cup about three times as wide as high. First 

 primary radials large, about as long as wide, three hexagonal, two 

 heptagonal. Second primary radials rather less than half as large as 

 the first, wider than long, hexagonal. Third primary radials smaller 

 than the second, about twice as wide as long, pentagonal, axillary, 

 and bear upon each upper slojnng side a single secondary radial. 

 The secondary radials are thick strong plates and stand out from the 

 calyx. There are ten ambulacral openings to the vault. Arms un- 

 known. 



The interradial areas connect with the vault, and the plates gradu- 

 ate into each othor. They are not uniform, and the plates vary in 

 llic regular areas from five to seven. In one area, there is one plate 

 followed by two, in the second range, and two in the third range, in 

 another area, there are three plates in the second range, and above 

 which there are three more. The azygous area is very large and con- 

 tains fifteen large plates. 'Die first one is in line with the first pri- 

 mary radials and Somewhat smaller than either of them. It is fol- 

 lowed by two plates in the second range, three in the third range, 

 and five in the fourth range, above which there are four plates that 

 may be classed in this area, though they interlock with those belong- 

 ing to the vault. 



The vault is depressed convex and covered with a few very large 

 tumid plates. The central plate is large and surrounded by seven 

 large plates. The azygous orifice is outside of the circle of seven 

 plates. The plates over the ambulacral channels are Large and those 

 in the slightly concave interradial areas smaller. 



The species is congeneric with Actinocrinus chouieauensis, and 

 neither of them are typical Actinocrinus. The calyx is that of an 

 Actinocriytus, and the vault is more Like that of an ( Agaricocrinus. 

 Under these circumstances, we think they should be referred to 

 Actinocrinus, as the differences are not sufficient to cause them to be 

 referred to a new genus. They do not belong to Physetocrinus even 



