422 



PELMATOZOA. 



canopy, from the bases of the arms, across the ventral aspect of the 

 calyx, as so many tunnels. During life these lodged both the food- 

 grooves and the water-vessels beneath them, and there is evidence 

 that the latter opened into a circular vessel surrounding the mouth 

 and representing the circular ambulacral vessel of the Echinoderms 

 generally. Hence in specimens of such forms, where the arms have 

 been detached (figs. 294-296), the upper side of the calyx is seen 



Fig. 294. — Calyx 

 of Actinocrimis ro- 

 tundus. 



Fig. 295. — Calyx 

 of A ctinocrinus Ko- 

 nincki. 



Fig. 296. — Calyx of A. Ver- 

 7iciiillanus. The arms are 

 wanting, and the apertures of 

 the food -grooves at their bases 

 are seen. 



to be covered with a plated dome, and the points of insertion of the 

 arms are marked by the openings of the food-grooves on their way 

 inwards to the concealed mouth. 



In the great family of the Cyathocrinidce, among the Palseo- 

 crinoids, the mouth and convergent food-grooves are concealed 

 from view by a vault which is chiefly composed of the " oral " 

 plates in the centre, together with the united covering-plates of the 



ambulacra (fig. 297, a). These 

 are all of a much less massive 

 character than in the forms 

 above mentioned, and are 

 readily destroyed. When these 

 tegminal plates have not been 

 preserved — as is very common- 

 ly the case — then the upper 

 surface of the calyx (fig. 297, 

 b) exhibits a large central peri- 

 stomial opening, to which the 

 five ambulacral grooves con- 

 verge, together with an excen- 

 trically placed and often pro- 

 boscidiform anus. In this family, the peristome is surrounded by five 

 large calyx-interradials, of which one (the "anal plate," fig. 297, a) 

 is excavated on one side, and corresponds with the anus. The 



B 



Fig. 297. — Upper surface of the calyx of Cy- 

 athocrinus malvaceus, showing the superficial 

 plating of the disc preserved (a) and the same re- 

 moved (b). am, Ambulacral grooves, in the one 

 figure roofed in by a double row of minute ossi- 

 cles, and in the other figure open ; a, " Anal 

 plate " ; o, Peristome ; an, Anus. (After Zittel.) 



