34 CALAMOCRINUS DIOMED.E. 



with the interradial plates are shown in Plate II. figs. 1, 2, Plate III. Figs. 

 1, 2, 5, Plate V. Figs. 1, 2, and Plate VI. Fig. 5. The same figures, and 

 Plate III. Fig. 4, Plate V. Fig. 4, and Plate VI. Figs. 4, 7, show the con- 

 nection of the same plates with the first, second, and third pinnules. The 

 thickness of the vault formed by these imperforate interradial plates is 

 shown in Plate III. Figs. 5, 6, 10, and Plate VI. Fig. 7. In the profile 

 figure of the lower brachials below the second pinnule (Plate III. Fig. 5), 

 the thickness of the wings of the arm joints is seen in section to their 

 junction with the upper face of the radials. It is to these faces that the 

 perisomic plates are firmly united. See also Figures 6-9 of Plate III. In 

 Figures 6, 7, we have the edge of the vault of the perisomic plates extend- 

 ing from the radial to the first pinnule ; in Figure 8, to above the second 

 pinnule. The lower part of Figure 7 of Plate V. shows the plating above 

 the radial to the first pinnule of the lower part of an arm corresponding 

 to Figure 5 of Plate III. ; the plating however conceals the inner parts of 

 the arm joints shown in Figure 5. In Figure 7 of Plate IV. we see the 

 plating in profile above the base of the first pinnule. Seen from the in- 

 terior, the connecting tissue conceals the outline of the imperforate plates, 

 and they appear more or less elliptical (Plate IV. Figs. 3-6). The outline 

 of the imperforate plates is completely concealed (Plate IV. Fig. 3) when 

 the upper part of the vault is seen from the inside. 



The sutures of the imperforate plates are very marked, while those of 

 the perforated plates are more or less indistinct, from the number of pores, 

 granules, and other irregularities of their surface, (Plate II. Figs. 1, 3, Plate 

 III. Figs. 1, 2, Plate V. Figs. 1, 4, Plate VI. Figs. 1, 4,) which become more 

 dense as they approach the food furrow. The spongy character of the' 

 perforated plates is seen in Plate IV. Fig. 8. 



The interradial plates merely abut against one another by their thick 

 edges; they are held together by the thickening of the .skin over the joints, 

 l)oth on the inner and outer surfaces of the calyx. The inner surface is 

 comparatively thickest, that of the outer surfiice being reduced to a mere 

 connecting film, the thick interradial plates having resorbed nearly the 

 whole of the perisomic skin, which in such genera as the modern Penta- 

 crinus forms the connective tissue in which the smaller disconnected plates 

 of the perisome are sunk, and form the indistinct pavement of the ventral 

 surface. 



The interradial plates of Calamocrinus are fully as stout and rigid as 



