PLAtE I 
Fig. 1. Agelacrinus holbrooki, James. A. Figure of type. B, Outline, side view of specimen, showing 
dome shaped elevation; figures accompanying the description of the species in the Journal of the Cincin- 
nati Society of Natural History, vol. x, p. 25, in 1887. C, anal region much enlarged, showing the squamous 
plates of the margin; the termination of the two posterior rays. Nos. 1 and 5, with both lateral and central 
covering plates; the anal pyramid, surrounded by small plates; copy of figure published by Clarke in New 
Agelacrinites, p. 189, in 1901, forming No. 40744, of the U. S. National Museum. D, Lateral outline of 
specimen No. 1004, in the James collection, at Chicago University, regarded as the type of the species 
although not oriented as in the published figure of the latter; the distal parts of the posterior rays. Nos. 
1 and 5, and part of the anal pyramid are preserved in this specimen; the drawing is intended to indicate 
the slumping of the theca owing to its supposed attachment to a slanting valve of Rafinesquina, the proxi- 
mal part of the right ray. No. 4, being directed toward the upper part of the slanting surface. E, five floor 
plates from the anterior ray of specimen 1004, the lower three pf which are parallel to the peripheral ring, 
and the upper two belong to the sanie ray, in a proximal direction; at the base of the drawing, the exposed 
parts of two covering plates are indicated; at the top, the basal extensions of three covering plates are rep- 
resented; transverse sections^ of two of the floor plates are presented. F, A lateral covering plate, and 
lateral view of the same to indicate its curvature, f 'om specimen 1004. 
Fig. 2. Agelacrinites beecheri, Clarke. Floor plates seen from below. Copied from figure accompany- 
ing the original description, in New Agelacrinites, in Bulletin 49, N. Y. St. Mus., on page 195, in 1901. 
Apparently only long enough for one lateral covering plate on each side of the floor plate. No. 4001-1, 
plastotype, N. Y. State Museum. 
Fig. 3. Agelacrinus faberi. Miller. A, lateral view; B, view from above; copies of the figures accom- 
panying the original description, in Journal, Cincinnati Soc. Nat. Hist., vol. xvii, on plate 8, in 1894. 
The type forms No. 8821 in the Faber collection, at Chicago Univ. (7, floor plates of the type, accompanied 
by a cross section of the same. 
Fig. 4. Agelacrinus warrenensis, James. A, natural size; B, same specimen enlarged; copies of 
figures accompanying the original description, in The Paleontologist, No. 7, plate II, in 1883. Regarded 
as young specimen of Agelacrinus cincinnatiensis, poorly preserved. 
Fig. 5. Agelacrinus pileus. Hall. A, central part of figure published by Miller and Faber, in Journal of 
Cincinnati Soc. of Nat. Hist., vol. xv, on plate I, in 1892. On that plate, the proximal part of the anterior 
ray is directed diagonally downward toward the right. In the figure here presented, this part of the ray is 
directed upward, and the rays are numbered. A part of the lower surface of the oral face of the theca is 
illustrated. Remnants of floor plates are seen at the proximal ends of rays 3 and 2. Most of the proximal 
floor plate forming that part of the rim of the substomial chamber which arches across ray 4, as seen from 
below, is missing. The proximal floor plates forming that part of the rim arching across rays 5 and 1 are 
entirely absent. The lateral covering?plates with their basal extensions are shown. Also three of the peri- 
stomial plates, the two anterior rhomboid plates and the posterior quandrangular plate, with their dove- 
tailing ridges, as seen from below. This specimen forms No. 8825 in the Faber collection, at Chicago Uni- 
versity. R, Peristomial plates and some of the adjoining plates of specimen No. 1192-2-A, belonging to 
the American Museum of Natural History. In this drawing L represents the left anterior rhomboid peri- 
stomial plate ; R, the corresponding plate on the right side ; P, the quadrangular plate on the posterior side of 
the peristomial slit. The basal plates of the rays are numbered so as to indicate the rays to which they 
belong. The proximal part of the anterior ray is directed toward the left, the position which it usually 
occupied when the animal rested on an inclined surface. The peristomial slit divided at its left end at 
plate Z, one branch passing between the two plates parked 2, and the other branch between the two plates 
marked 1. In a similar manner, the slit divided at its right end at plate Y. A duct may have opened near 
the meeting point of plates P, 5, and X. X is merely one of the interambulacral plates. In the case of the 
anterior ray. No. 3, several of the lateral covering plates are drawn as though they exposed also the basal 
extensions of these plates, but the latter details were added from the specimen represented by Fig. 5a, on 
this plate. C, one of the lateral covering plates of the specimen represented in Fig. 5A, on this plate, as 
seen from below, showing two striae at the base, paral el to the length of the ray; also a Uteral view of the 
same, to show its curvature. D, lateral view of a covering plate belonging to the opposite side of the ray. 
Fig. 6. Agelacrinus cincinnatiensis, Roemer. A, lateral covering plate with diagonally directed basal 
extension, as seen at the angle between two rays, in specimen No. 13266- 1-c, in the American Museum 
of Natural History. B, three lateral covering plates, and a lateral view to indicate the curvature of the 
latter, from specimen No. 1008 C, in the James collection, at Chicago University. _ C, two floor plates, 
showing a narrow longitudinal groove on each side, from a specimen in the Geological Museum of Ohio 
State University; also a transverse section of the same.^ D, one of the large plates forming the inner band 
of the peripheral ring, showing the three short vertical ridges near the base of the inner face ; from specimen 
13266-1-s, of the American Museum of Nat. Hist.; F, the edges of several of these plates, as seen from 
the interior of the theca, showing the location pf these vertical ridges in the spaces left between the lateral 
edges of the adjacent plates, thus giving rigidity to the inner band of the peripheral ring; from specimen 
13266-1-r, in the same museum as the last. 
Fig. 7. Streptaster septembrachiatus,_Miller and Dyer. A, view of central part of oral face of theca, as 
seen from below, including the substomial chamber and the adjacent parts of the rays. The rays are 
numbered. There appears to be a deep cavity at the posterior border of the substomial chamber, toward 
of which, as seen from below, there is a quadrangular plate with broad groove ascending it on the left. In 
the case of the rays, only the floor plates, as seen from below, are indicated. The peristomial plates, as 
seen from below, are nob sufficiently defined to be represen bed with accuracy The anus was located close 
to the substomial chamber, between rays 5 and 1 . A part of the surrounding interambulacral area appears 
to be preserved. B, three floor plates as seen from the side, supporting three vertical palisade like lateral 
covering plates; also an imaginary view of these three floor plates as seen from the top, with facets for the 
support of two lateral covering plates on each floor plate. 
Fig. 8. Thresherodiscus ramosa, Gen. et. sp. nov. Parts of the proximal portions of rays 3, 4 and 5, 
drawn so as to indicate the usage of certain terms in the accompanying descriptions. The basal parts of 
the arms are numbered ; / 1 indicates the floor plates in the case of the two primary branches of the anterior 
ray. No. 3 ; 5 indicates the small bordering interambulacral plates adjoining the floor plates of the anterior 
ray and the lateral covering plates of one side of the rignt ray. No. 4; ia indicates the location of the large 
central interambulacral plates, within the zone of much smaller bordering interambulacral plates; C, 
indicates the two rows of lateral covering plates on one of the branches of the right ray. No. 4. The super- 
numary covering plates along the median line of the ray, between the lateral covering plates, are also indi- 
cated in the drawing, without any effort at accuracy of detail, but are not designated by any letter. Only 
enough is shown in the drawing to illustrate the usage of the terms here indicated. 
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