110 K. ETHERIDGE, JTTX., OX ASTKOCRIXITES. 



into several orders, the first two of which are the Cionacineti 

 (Austin), or those forms with a jointed flexible stalk, and the 

 Liber idee (Austin), the latter containing the family in question. 



The following remarks are devoted to a consideration of the sys- 

 tematic position of Astrocrinites ? Benniei with regard to the various 

 orders of the Echinodermata as at present recognized. I believe I 

 am correct in stating that throughout the Echinoidea, Asteroidea, 

 and Blastoidea the quinqueradial arrangement is steadily maintained, 

 and that in the Crinoidea, although the arms become much mul- 

 tiplied, they are primarily from five to ten in number. On the 

 other hand, in the Cystoidea (e. g. Apiocystites, &c.) the radii are 

 sometimes reduced to four ; but although such is the case, they can 

 hardly be compared to the radii of A. ? Benniei ; for in Apiocystites 

 they are only recumbent arms, whereas in the latter they are pseud- 

 ambulacra imbedded in the plates of the test. However, A. 1 Benniei 

 so far corresponds with some Cystideans ; but, on the other hand, 

 there are not any organs similar to the pectinated rhombs of that 

 Order. 



The absence of a stem or column for attachment tends to separate 

 this species from the Crinoidea, Blastoidea, and Cystoidea, although 

 we know that in the adult condition some Crinoidea are free, and 

 that certain Cystideans (Agelacrinites &c.) are asserted to be without 

 any column ; whilst in another, Lepadocrinus, there is evidence to 

 show that it was free, or that its means of attachment were not of 

 a permanent description. 



A. tetragonus, Austin, has been described as possessing a madrc- 

 porifonn body, which, if it exists as described, would indicate 

 Asteroid or Echinoid affinities ; there is, however, no trace of such 

 an organ in A. ? Benniei. Purthermore, in the Asteroidea the ske- 

 leton is composed of a large number of small plates united by mem- 

 brane ; and when a second aperture in addition to the mouth is 

 present, it is dorsal and nearly central. In the form under con- 

 sideration the arrangement of the plates of the calyx is quite different 

 from the foregoing ; and both apertures, which are constant, are on 

 the ventral surface. 



It appears to me that the forked plates (figs. 7 & 7*) into which 

 are received the apices of two of the pseudambulacra, correspond with 

 the forked " radial " plates of the Blastoidea, although there is this 

 curious divergence from the latter type : — If we take a Pentremite 

 for example, any lobe-like projections existing in the general peri- 

 phery are caused by the projection of that part of the radial plates 

 into which are received the apices of the pseudambulacra (a, fig. 27), 

 whereby the suture or union of each prong of the forked plates 

 with its neighbour lies more or less in an angular concavity or re- 

 entering angle (b, fig. 27) ; in Astrocrinites this arrangement is 

 reversed, the pseudambulacra all lie in deep concavities between the 

 convex and projecting lobes, so that in this case the line of union 

 of the contiguous prongs of the forked plates lies on a convexity, 

 instead of in a concavity as in the Pentremite. 



Mr. Billings has pointed out that in the Pentremite the forked 



