740 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxii. 



mesentertj, especially the dorsal mesentery, the sheet of transparent tissue joining the 



oesophagus and intestine to body wall. The anterior portion of alimentary canal 



is slung by the dorsal mesentery to the middorsal (interradial) line of body wall. 



(Plate LX XX, fig. 1, me.) 

 miliary granules, simplest form of calcareous deposits, namely, more or less irregular 



grains. 

 j>apill!V, ambulacral appendages in which the sucking disk is absent and the terminal 



plate absent or rudimentary. 

 pedicels, tube feet, or locomotor organs, having a ti-rminal sucking disk. 

 peltate, said of tentacles having a circulir, flattish, or convex crown. 

 pinnate, of tentacles having the branches occurring regularly along the sides in two 



opposite series and without subdivisions. (Plate LXVI. ) 

 plates, thin, flat, wide, usually perforated deposits. (Plate LXXIX, fig. 1, 6.) 

 Polian vesicle, cul-de-sac, or reservoir, connected with ring canal of water vascular 



system. (Plate LXXX, fig. 1, p. v. ) 

 posterior prolongations of calcareous ring. (Plate LXXIX, figs. 2, 3. ) 

 radial muscles, the five, usually double, bands of muscle running from end to end of 



the animal along the five radii. 

 radial pneces, see calcareous ring. (Plate LXXXII, fig. 1, r.) 

 respiratory trees, when present, a pair of long, much-branched outgrowths of wall of 



cloaca, lying in body cavity, usually unequal in length. The left is frequently 



associated with the rete mirabile. (Plate LXXIV, fig. 1, r. ) 

 rete mirabile, complex plexus of blood vessels between the dorsal vessel (marginal 



vessel of the rete mirahUe) and the lacunar network of the alimentary canal. Some 



of the numerous small retia mirabilia form webs around the terminal ramifications 



of the left respiratory tree. 

 retractor muscles, anterior free portion of radial muscle attached to end of radial piece 



of calcareous ring and serving to retract tentacles and anterior portion of l)odyinto 



body cavity for protection. 

 rods, rod-shaped deposits. (Plate LXXV, figs. 1-5.) 

 rosettes, calcareous deposits in the form of rods more or less irregularly and profusely 



branched. (Plate LXVII, figs. Ic, 4a; Plate LXXX, fig. If.) 

 spire, upright portion of a table. (Plate LXVII, fig. 2a; Plate LXXII, figs. la-e. ) 

 supporting rods, calcareous rods in walls of tentacles, papillfe, and pedicels. (Plate 



LXVIII, fig. 4; Plate LXIX, fig. Ig.) 

 table, a perforated plate having a projection, made up of several rods more or less 



joined together, rising pei'pendicularly from the middle. (Plate LXVII, fig. 2a.) 

 tentacle ampidla;, vesicles of the ambulacral system connected with the tentacles and 



lying in the body cavity, around the calcareous ring. 

 tentacles, modified ambulacral appendages surrounding the mouth, often much 

 • branched. (Plate LXVI, <.) 

 wheels, wheel-shaped deposits. (Plate LXXVIII, fig. 1.) 



