1885.] NATURAL SCIENCES OF PHILADELPHIA. 241 



ventral surface arc much more delicate, and consist of a centra! 

 plate, large proximals, and several rows of covering pieces, 

 without the intervention of either anambulacral or interradial 

 pieces. It would lie difficult with the utmost stretch of our 

 imagination to recognize in the former figures either proximals 

 or central piece, which, as admitted by Carpenter, are present in 

 all these Crinoids, and we think there can be little doubt that 

 the two sets of figures represent different parts of the animal, the 

 one the disk, the other the vault, and that the one covered the 

 other. A similar opinion was evidently entertained by Zittel 

 (Hanclb. d. Paheont., i, p. 357), who stated that Crotalocrinus pos- 

 sessed five " grosse Oralplatten, bald unter der Decke, bald 

 ausserlich sichtbar." According to our interpretation, the calyx 

 of the Crotalocrinida- extends ventrally to the oral pole, and 

 the ambulacra, central piece and proximals are subtegminal, 

 covered by interradial plates, which extend out to the lower rows 

 of covering plates and side-pieces (Icon. Crin. Suec, PL 7, fig. 6, 

 and PI. 25, fig. 15). A similar condition probably prevailed in 

 the Ichthyoerinida?, with which the Crotalocrinid;e have close 

 atlinities. 



In the Ichthyoerinida*, inter radials have been observed only 

 at the dorsal side, where they are subject to many irregularities. 

 In some of the genera they are always present, in others entirely 

 absent ; while there are still other genera and certain species, in 

 which they are occasionally undeveloped dorsally. The interra- 

 dials of the Ichthyocriniclse are united by ligamentous articulation 

 among themselves, and also laterally with the radials, as shown by 

 the presence of deep fossa 1 at the sides of the plates (PI. .">, fig. 5). 

 The mobility in the test, resulting from this structure, led us 

 formerly to state that the ventral covering, which is so rarely 

 preserved. " perhaps " consisted of a " soft or scaly integument." 

 The word " soft " was ill-chosen, and did not express our real 

 meaning, we should have said, as we did in other places," pliable." 

 There is nothing to indicate a membranous surface structure, but 

 the pavement evidently was pliable in conformity with the con- 

 dition of the test at the dorsal side. In Onychocrinus exsculp- 

 tus, the only [chthyocrinoid in which portions of the ventral 

 covering have been observed. Lyon and Casseday found in the 

 radial regions rather large, alternately arranged plates (Amer. 



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