EXPLANATION OF THE PLATES. 



PLATE I. 



Fig. 1. Platycrinites ljevis, a to «, exclusive of k. 



II. — lateral aspect she\\-ing the articulations of the ray joints. 



I). — minute specimen exhibiting the change in the form of the column, rays, &c. 



c. — portion of column shewing the bases of auxiliary side arms. 



d. — column exliibitmg the gradual change from circular, alternately larger and smaller 

 joints, with radiating striae on their upper and inferior articulating facets, to 

 joints of equal thickness and elliptical form, mth transverse ridges and without 

 radiating striae. 



e_ — lateral aspect showing the proboscis, rays, tentacula, part of the column attached, &c. 



f. — mcso-plate, interscapular of MiEer. 



(/. — bifurcation of rays exhibiting the arrangement of their joints. 



li. — perisomic plate with the base of rays attached. 



/. — perisomic plate sho\ving the excavation for the attachment of the ray joints. 



/. — proboscis, or oral tube, exhibiting the beautiful arrangement of the proboscidial plates. 

 — enlarged -view of the apex of the proboscis. The plates conceal the oral apertm-e. 



m. — minute specimen, with rays <and tentacula. 



,,. — dorso-ccntral plate exhibiting the radii for the attachment of the column. 



Fig. 2. Platycrinites spinosds, o to s, including k. 



/,-. — lateral aspect exhibiting the spiniform abdominal plates, with the same magnified. 

 fj_ — lateral aspect sho-«Tng the base of the proboscis, rays, tentacula, attachment of the 



column, &c. 

 J). — proboscis exhibiting the spiu'-like protuberances near the apex. 

 0. — lateral view of the abdominal bulb, and rays. 

 r. — cuneiform, and other ray joints, mth their articulating facets. 

 s. — tentacula, with the manner in which the double series of ray joints fit into each 



other. 



PLATE II. 



Fig. I. Platy'crinites mvcronatus, a to /. 



a. — ^^-iew of the apex exhibiting the abdominal plates \yiih theii- central points, as also 

 the ca\ity where the lateral mouth was situated. 



