354 PROCEEDINGS OF THE ACADEMY OF [1S90. 



crinus, and probably the Ichthyocrinidae generally, in which mouth 

 and food grooves are exposed, as we now knuw from actual observa- 

 tion' ; but in the case of Reteocriaus and Glyptocrmus he had no 

 proof beyond a superficial resemblance of the plates. Similar plates 

 occur among species of the Actinocrinidae and Meloerinidae in the 

 same genus, together with species with large plates, and all of these 

 must be perisomic or none of them. 



We now take up the Inadunata, which we have sub-divided in 

 Pt. Ill of the Revision, into Larviformia and Fistulata. 



The Inadunata Larviformia were regarded by us as representing 

 the larval state of the Crinoids in a persistent form. The most com- 

 plex Actiiiocrinoid or Cyathocrinoid must have ])assed in early life 

 through a stage in which it closely resembled Haplocrinus, when^ 

 the entire calyx consisted of basals — sometimes underbasals — radials, 

 and orals. To these plates subsequently in Symhathocrinus an anal 

 plate was added, but this disappeared in the later AUagecrinus. 

 The three stages here alluded to, which are represented phylogeneti- 

 cally by distinct genera or families within the group, recur in the 

 embryonic development of recent Crinoids. 



The most characteristic embryonic feature of this group, is the 

 covering of the ventral side by orals only. The plates of Haplocrinus 

 were called by us orals in Pt. II of the Revision ; but when 

 later on we thought we had discovered centrally within this ring of 

 plates another plate, we regarded this as the representative of the 

 orals (Rev. Pt. Ill, pp. 31 to 34), and those surrounding it as inter- 

 radial plates. Subsequently discovering conclusively that such a 

 plate does not exist, we admitted our mistake^ and recognized the 

 scheitelplatten as orals. The Larviformia, therefore, have neither 

 interradial nor interambulacral plates, and that they were in a low 

 state of development is seen also by their arm structure. By far the 

 iQost of them have but one arm to the I'ay, and their arm joints are 

 immovably united by suture, but the union between radials and 

 brachials is by articulation. Even in Haplocrinus, probably the 

 lowest known form of this group, the radials are perforated. The 

 earliest Larviformia known to us are from the Upper Silurian, but 



1 Discovery of the Ventral Surface of Taxocrinus and Haplocrinus, and con- 

 sequent Modifications in the Classification of the Crinoidea, by Charles Wachsmuth 

 and Frank Springer; Proc. Acad. Nat. Sci. Fhila., 1888, pp. 837-363. 



■^ Ibid., p. 340. 



