16 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Mouth angle plate. 



See Oral armature. 

 Ocular plate. 



A single large, grooved eye-plate occupying the distal ends of rays and support- 

 ing a sensory tentacle at the base of which occurs the eye-spot. They appear in 

 the larval stage as the primary radials and with growth pass outward, remain- 

 ing at the tip of the rays as the oculars. They are also known as terminals. 

 These large plates are not present .as such in early Paleozoic genera, and are 

 unknown before the Carboniferous. 

 Oral. 



See Actinal. 

 Oral angles. 



The interradial actinal areas around the mouth. 

 Oral armature. 



The pairs of plates, usually five in number, composing the apices around the 

 central actinal opening or mouth. In most Paleozoic forms the armature 

 consists of the proximal modified adambulacral plates. These pieces are also 

 known as Mouth angle plates. 



In some Paleozoic forms (Hudsonaster) there lies in front of each pair of mouth 

 angle plates a single plate; this is known as the Torus. 



Gregory (1900, p. 241) writes that "the Oral Skeleton (or actinostomial ring) 

 consists of a solid calcareous ring around the mouth. It is composed of thirty 

 plates in a quinqueradiate starfish, there being always six times as many plates 

 as there are rays. Each segment of the oral skeleton consists of two pairs of 

 ambulacral, and of one pair of adambulacral ossicles. In Asterias [a cryp- 

 tozonian] the ambulacral plates are more prominent than the adambulacrals, 

 and project into the oral cavity." 



When the ambulacral elements are the more prominent, the oral skeleton is said 

 to be of the ambulacral type. This is only present in cryptozonians. When 

 the adambulacral ossicles are the most prominent, the oral skeleton is of the 

 adambulacral type. This latter construction is the more primitive and occurs 

 in all the Phanerozonia, but is also present in some of the cryptozonians. 

 Ossicles. 



See Plates. 

 Papulae. 



In living Asterias, a cryptozonian, from between the spicular plates there rise 

 from all parts of the external surface short and small integumentary protuber- 

 ances that are used for respiration. In the more heavily plated Phanerozo- 

 nia they are limited to the abactinal surface enclosed between the supramar- 

 ginal plates. It is probable that papulae were present in all Paleozoic forms 

 having rounded or spicular ossicles, issuing in the open spaces between the 

 plates. They probably were absent in the earliest closely plated starfishes, 

 such as Hudsonaster. See Csecal pores. 

 Paxillse. 



Minute calcareous processes arranged around large spines. None are known 

 in Paleozoic genera. 



"Another type of spines occurs as part of the structures known as 'paxillse.' 

 Each paxilla consists of a thick plate supporting a number of short, calcareous 

 pillars, the summit of each of which is covered by a group of small spines. 

 In some Phanerozonia * * * the paxillse occupy almost the whole abactinal 

 surface of the Asteroid" (Gregory 1900, p. 247). 

 Pedicellarids. 



Pincer or scissors-like calcareous appendages, attached to the spines, the plates, 

 or the skin, which keep the body-wall clean of parasites. None have as yet 



