KEVISION OF PALEOZOIC STELLEROIDEA. 17 



been detected with certainty in Paleozoic genera. In the primitive Recent 

 forms they are also absent, the integument being protected by an abundance 

 of closely set spines. 



"The Pedicellarise of Asteroids are of four main types. The simplest form con- 

 sists of a row of pairs of small, sessile, opposable spines; these are the 'pseudo- 

 pedicellariae.* The members of the second set are ' sessile.' The next advance 

 is the development of a stalk; of these pedunculate pedicellariae there are two 

 varieties: (1) the 'forficiform,' in which the two hooks are attached to the near- 

 est end of the basal plate nearest to them; (2) the 'forcipiform,' in which the 

 two hooks cross one another and are attached to the end of the basal plate far- 

 thest from them " (Gregory 1900, p. 247; also see Verrill 1914, pp. 25-34). 

 Perradial. 



The area along the center of the rays. The ambulacra are perradial in position. 



See Interradial. 

 Plates. 



Some writers restrict the term plates to the five primary radials, five interradials, 

 and the central disk piece, and refer to all the other calcareous parts as ossicles. 

 The word plates is here used in the widest sense, and as interchangeable with 

 ossicles. For the sake of brevity the plates will be often referred to as margi- 

 nalia, radialia, etc. 

 Podial openings. 



The rounded openings between the ambulacral plates for the protrusion of the 



locomotor organs, the podia or water- tube-feet. See also Ambulacral. 

 Primary radial. 

 See Radial. 

 Primary skeleton. 



The skeleton of a starfish is made up of primary and secondary ossicles. The 

 primary skeleton consists of the longest inherited and the first appearing plates 

 in the young, as the ambulacral, adambulacral, marginal and radial columns, 

 plus the primary pieces of the disk. All the other ossicles inserted between 

 these are of the secondary skeleton. 

 Radial 



Refers only to the prominent abactinal primary plates holding a radial position. 

 Where present, they form columns of continuous reticular or separated radialia, 

 situated along the radial center of the rays. Proximal radials are those on or 

 near the disk and should not be confounded with the primary radials, the 

 probable homologues of the radials in crinids. These plates are also known as 

 median dorsals, dorsals or carinals; also as radialia. 

 Rays. 



The radial "arms " of starfishes. These are hollow and contain the digestive, 

 reproductive, and water-vascular systems and other organs. The rays merge 

 gradually and without sharp demarcation into the central disk. 

 Respiratory pores. 



See Csecal pores. 

 Secondary skeleton. 



See Primary skeleton and Accessory plates. 

 Spines. 



See PaxillsR and Pedicellarids. 

 Supramarginal. 



See Marginal plates. 

 Terminals. 



See Ocular plate. 



