102 PROCEEDINGS OF THE ACADEMY OF [1887. 



It may not be out of place to mention in this connection that in 

 IIa])locrimL8 there appear radially between the five large ventral 

 jjlates, upon their lateral edges, five conspicuous grooves (figs. 4 and 

 5), which were regarded by Prof. Zittel (Handb. d. Palaeont, I, ^. 

 347) as ambulacral furrows. Similar grooves exist in Cyathocrinus, 

 Stephanocrinus and other Inaduuata along their intei'radials, and in 

 all of them the grooves are occupied by the ambulacra. The simi- 

 larity between these grooves, no doubt, induced Prof. Zittel to give 

 to those of Hcvplocrinus the same interpretation. Unfortunately, 

 however, the central plate of Haplocrvnus, as plainly seen in our 

 specimens, does not occupy exactly the same level as the upper an- 

 gles of the five large plates, but lies (Fig. 4) below their level and 

 between them, just as if it were being pushed from within outward 

 so as to separate the five plates at the central space. The peculiar 

 position of the centi'al plate demonstrates, we think beyond any 

 doubt, that the ambulacra of Hajilocrinus could not have been ex- 

 posed ujion this groove, but at the same time it appears to us that 

 these grooves, which occupy relatively the same position toward 

 surrounding plates and the peristome, and are formed in a similar 

 manner, must represent morphologically the same grooves, which 

 are occupied in higher developed types of this group by the ambul- 

 acra (fig. 3). Supposing that Hapilocrinus, as we find it in the 

 fossil state, were but an embryonic stage of the species the genus 

 has been regarded a permanent larval form of the grouji we think 

 we might safely assert from the phylogeny of the Palaeocrinoidea 

 generally, that in the growing animal the central plate was pushed 

 outward so as to appear at a level with the five interradials ; that 

 subsequently by the growth of the dorsal cup, and the widening of 

 the peristomial area, proximals appeared around the central piece ; 

 and that at last the ambulacra were pushed out to the surface to 

 occupy the radial grooves, which were present already in the young 

 Haplocrinus. The different stages to which we here have alluded 

 are well represented in palaeontological times throughout the Inad- 

 unata, and not only among them, but also among the Camarata 

 under very similar conditions. 



The Camarata or Coadunata differ from the Inadunata in having 

 their proximal arm joints incorporated into the calyx by the up- 

 ward growth of interradials ; Avhile in the Inadunata the arms re- 

 main free from the first radial, and they have but one interradial 

 which is disposed ventrally. That all Camarata passed temporarily 



