416 
Aug. F. Foerste 
adjacent plates, are badly weathered. As far as may be determined 
from all the specimens at hand, the peristomial plates of Agela- 
crinus cincinnatiensis agree with those of Agelacrinus pileus in the 
presence of a rhomboid left anterior plate, a rhomboid right 
anterior plate, and an irregular, so-called quadrangular, posterior 
plate; along the lower part of the right hand margin of the latter 
the border is raised, and at the angle at which the posterior plate 
is joined by the first lateral covering plate of the right posterior ray 
and by the adjacent interambulacral plate, there may have been 
the opening of some duct. However, the long, narrow plates, 
which in Agelacrinus pileus are intermediate between rays 1 and 2, 
and between rays 4 and 5, have not been identified, and the first 
covering plate on the contrasolar side of the left posterior ray, in 
Agelacrinus cincinnatiensis, frequently is long and narrow, and 
parallel to the adjacent oblique left margin of the posterior peri- 
stomial plate, instead of resembling th'e immediately following 
lateral covering plates of the same ray, as in Agelacrinus pileus. 
The peristomial area of Streptaster is unknown. Judging from 
the close similarity of the covering plates in some of the speci- 
mens referred to Agelacrinus pileus to those of Streptaster it is 
suspected that, when the peristomial plates of Streptaster are known 
these also will be found similar to those of Agelacrinus pileus. 
In Cystaster granulatus, the various peristomial plates recog- 
nized in Agelacrinus pileus (R, L, R, Y, Z, in Fig. 5B, on plate 
I) may be identified. The two anterior peristomial plates are 
strongly V-shaped. The posterior peristomial plate also is 
strongly grooved along the median line, as though it originally 
consisted of two distinct plates. 
18. Floor Plates of Devonian and Carboniferous 
Agelacrinidae 
The plates beneath the ambulacral grooves are known as the 
floor plates. These floor plates have been known hitherto from 
only a few species among the Agelacrinidae. 
In Haplocy stiles rhenana, Roemer, from the lower Devonian of 
the Rhine, there was only a single row of these floor plates. The 
species has been refigured by Jaekel {Stammesgeschichte der 
Pelmatozoen, 1899, plate III, Fig. 3), and, according to Clarke, is so 
closely related to the American Echinodiscus or Lepidodiscus, that 
eventually the name Haplocy stites may displace one of these terms. 
