1885.] NATURAL SCIENCES OP PHILADELPHIA. 285 



vault of an Actinocrinoicl. A total resorption of all interradial 

 plates, dorsally and ventrally, and also of the proximals, would 

 reduce an Actinocrinoid, or Platycrinoid, essentiall} T to the 

 condition of a Neocrinoid that has its lower arm joints connected 

 by perisome. The fact that the perisome is continued under- 

 neath the proximals, and extends to the central piece, tends to 

 prove that the latter, and not the proximals, represents the oral 

 pyramid, as these plates surround the peristomial area but do 

 not cover it (PI. 1, fig. 6). It further proves that the inter- 

 radial plates of Platycrinus, Glyptocrinus and Reteocrinus cannot 

 be partly plates of the calyx and partly pcrisomic, but must 

 be either the one or the other. If the Reteocrinidse had lived 

 in Carboniferous times, and the Actinocrinidse in the Lower 

 Silurian, there might be a possibility that in the former the 

 interradials, dorsally and ventrally, as well as the summit plates, 

 had been resorbed ; but as they comprise one of the earliest 

 known groups, this interpretation need not be considered, and we 

 can only regard those plates as ill-defined interradials. 



We find it difficult to believe that the so-called "interradials " 

 of Guettardicrinus, and Apiocrinus i-oissyanus and allied species, 

 are homologous with the calyx interradials of an Actinocrinoid ; 

 but regard all those pieces as enormously developed perisomic 

 plates. That they are somewhat heavier pieces and more regu- 

 larly arranged than those plates usually are, is not sufficient to 

 make them calyx plates, as they evidentlj- adapted their con- 

 ditions to surrounding parts, and are therefore thick plates from 

 necessity, in order to fill the deep edges of adjoining radials. 

 De Loriol, in the Paleont. Franc, on p. 2*72, describes them in Apio- 

 crinus roissyanus as follows: Pieces interradiales nombreuses, 

 tres inegales, elles varient dans chaque espace interradial dans 

 le nombre et l'arrangement. Presque toujours la serie commence 

 par une piece unique, hexagone ou heptagone, qui est la plus 

 grande, quelquefois fort grande. . . . Au-dessus il y a deux, trois, 

 et meme quatre pieces plus petites, irregulieres, polj-gonales," 

 etc. This description does not apply to calyx interadials, among 

 which the first plate is always very regular, and the first row 

 never consists of two plates, nor the second variously of two, 

 three or four pieces. This irregularity seems to have puzzled 

 Carpenter, for, on p. 183 of the Challenger Report, he suggests 

 that perhaps the " smaller interradials were perisomic plates." 



