REPORT ON THE CRINOIDEA. 43 
interradial area is wider than the other four “with a conspicuous row of decidedly 
larger and more prominent pieces along the median part.” Billings’ gave a good 
figure of this in Reteocrinus stellaris, and spoke of it as follows :—“ If this series of 
joints constitute a true arm there must be six arms in this species.” Miller, who has 
examined the original specimen of Reteocrinus stelluris, describes it thus—“ Azygous 
interradial area covered by a large number of plates, probably one hundred or more, 
very unequal in size, the middle row being decidedly larger and more prominent than 
the others, so as to form a ridge up the middle. The plates in this row, however, 
do not rapidly diminish in size and fade out in their distinctive character before reaching 
the top of the vault; on the contrary, they are longer than the primary radials, four of 
them reach nearly as high as the secondary radials, and while the specimen is not 
preserved above this, enough is disclosed to the palzontologist to show that this series 
continued up the face of a proboscis that extended, may be as far, or farther, than the 
arms and the pinnules.” 
In default, however, of further evidence I prefer to believe that the middle row of 
plates in the anal area of Reteocrinus stellaris was of the same nature as, though perhaps 
on a larger scale than, that of Reteoerinus nealli, which Miller describes as follows :— 
“ Azygous interradial area covered by fifty or sixty plates, very unequal in size, the 
middle row being decidedly larger and more prominent than the others, so as to form a 
ridge up the middle, while the other smaller and less prominent ones are crowded in, 
irregularly, on each side. The plates in this middle row, however, have no uniformity in 
size or shape; the first one is large and elongated, the fourth is small and subquadrate ; 
and the row has become almost obsolete at the sixth plate, where all are nearly of the 
same size and scarcely distinguishable from the minute pieces which cover the flattened 
vault, and with which they unite.” The figures of this type in the Paleontology of 
Ohio (vol. i. pl. ii. figs. 3b, 3c) illustrate this description admirably, the original 
specimens having doubtless been seen by Miller; while the figure of Reteocrinus 
subglobosus on the same plate (fig. 2c) shows the incorporation into the body of a 
pinnule borne by one of the secondary radials. This pinnule is closely surrounded by 
the minute interradial plates, but may be distinguished from them at its origin just as 
the anal appendage is. This condition is still better shown in Reteocrinus richardson, 
Wetherby, which has two “fixed pinnules” in the anal interradius, one on either side of 
the median appendage. All three are “soldered” together by the minute irregular plates 
which pass insensibly upwards into those of the so-called “vault ;” and the ordinary 
pinnules on the lower parts of the arms after the last axillary are united in just the same 
way.” This condition recurs constantly in the Liassie Hatracrinus and in the recent 
1 Decades of the Geological Survey of Canada, vol. iv. p. 64, pl. ix. fig. 4a. 
2 Deseriptions of New Crinoids from the Cincinnati Group of the Lower Silurian and the Subcarboniferous of 
Kentucky, Journ. Cine. Soc. Nat. Hist., vol. ii. pl. xvi. figs. 1, la. 
