Agelacrinidae and Lepadocystinae 
429 
the chamber, this quadrangular plate is ridged somewhat like a 
letter W, the sides of the letter abutting against the thickened 
inner margins of the adjacent proximal floor plates. Toward the 
two grooves on the inner side of this posterior quadrangular plate, ^ 
one on each side of the median ridge, project the strong median 
ridges of two plates, which, from interior view, have a triangular 
form, with the broad base against the sutures between the ante- 
rior and right proximal floor plates, and between the anterior and 
left proximal floor plates. These plates probably are merely the 
interior views of the two rhomboid plates (R and L) seen on the 
exterior view of peristomial area, and the vertical ridging pre- 
vents lateral displacement. 
This leaves to be accounted for a peculiar margined depression 
along the proximal part of the right hand margin of the right 
posterior ray (No. 5), as viewed from below. This impression 
involves the two proximal covering plates on the left side of the 
right posterior ray, where adjoining the right margin of the large 
posterior peristomial plate, as seen from above. Possibly a duct 
passed by this path, but its presence could not be verified with 
confidence. (Plate I, Fig. 5A.) 
There is no evidence of the base of this substomial chamber or 
cavity ever having served as a support of the theca, as suggested 
by Miller and Faber. It probably was underlaid by the central 
fleshy aboral face of the specimen. It served chiefly to strengthen 
the central parts of the upper part of the theca, in the peristomial 
region. 
Moreover, there is no indication of any passage between the 
mouth and the anus. The gut appears not to have had any special 
protection apart from the rest of the soft parts of the animal. 
Moreover, the direction of torsion of the gut is unknown. 
28. The Central or Substomial Cavity of Streptaster 
Septembrachiatus 
The lower surface of the upper face of a theca belonging to some 
species of Streptaster is exposed fairly well on a rock fragment 
found 8 feet be'ow the top of the Elkhorn member, in the upper 
part of the Richmond, at a small waterfall wed of the home of 
John Miller, a short distance west of the Union road and north 
of the Eaton pike, about three miles west of Dayton, Ohio. 
