250 PROCEEDINGS OF THE ACADEMY OF [1885. 



appear to occupy an intermediate position between the heavily 

 vaulted Platycrinidae and the more thinly plated recent forms. 



We have shown already that neither the small irregular plates 

 in Glyptocrinus, nor any of the interradials of Platycrinus, are 



perisomic plates, and this in itself is a strong proof, that the 

 structure, which occupies relatively the same position in the allied 

 genus Reteocrinus, cannot represent a totally different thing. 

 Carpenter leaves us in doubt whether the so-called disk of Beteo- 

 crinus and Xenocrinus begins at the basals, where those minute 

 irregular pieces commence, or at the equatorial zone, as he be- 

 lieves it does in Glyptocrinus. It seems to us, if he had not 

 meant the whole interradial series, he would not have made a 

 comparison of these parts with those of the Liassic Extrac?'imix 

 and recent forms without interradials, but would rather have 

 -elected Thaumatocrinus, in which interradials are present. 

 He also indicates it by his remarks on the fixed pinnules of 

 Reteocrinus, which, as we know, are located dorsally, and which 

 he says (Chall. Hep., pp. 39, 40) are soldered together by the 

 minute irregular plates, winch pass insensibly upwards into the 

 plates of the so-called vault, and further: u This condition recurs 

 constantly in the Liassic Exlracrinus, and in the recent Penta- 

 crinidae and Comatuhv ; and I see no reason to believe that the 

 minute interradials of Reteocrinus are in any way different from 

 those of the Neocrinoids. But I regard them as perisomic plates, 

 continuous with those of the disk above, which was in no sense a 

 vault like that of the Actinocrinidae." 



According to this, if we understand him correctly, the calyx in 

 the Reteoorinidae consisted only of basals, underbasals and radials, 

 which latter throughout their full length were enclosed by peri- 

 somic plates. This would be a very peculiar condition for one of 

 the earliest known Crinoids, if we admit that the Paheocrinoids 

 are developed from a lower morphological level than the Neocri- 

 noidea. In support of it Carpenter has no other proof than a 

 superficial resemblance in the form of the plates. There is 

 nothing to show that any of the plates were perforated, there is 

 no external mouth, no food grooves, nor plates that could possibly 

 be considered as covering pieces. All the plates dorsally and 

 ventially, even those extending to the free rays, have the same 

 irregular arrangement. The ventral surface of Reteocrinus is 

 almost identical with that of Glyptocrinus decadactylus, which 



