98 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Postradial series. — All the ossicles, collectively, whic.li arc borne by a single radial. 



Prehracliial stage. — See Cystid stage. 



Primary anteroposterior axis. — See Axis la. 



Primary arm. — A term sometimes used to designate the IBr series. 



Primary cords. — Tlic live nerve trunks wliich arise from the central capsule (see 

 figs. 63, 64, p. 89, and pp. 350-354). 



Primary groove irunJcs. — See Groove trunks 1. 



Primary interradials. — See Interradials 1 . 



Primary skeleton. — The Radial skeleton, plus the centrale, the ccntrodorsal, or the 

 cohimn. 



Primihrachs (IBr). — The ossicles following the radials up to, and including, the first 

 post-radial axillary ; in case the arm docs not divide all the brachials arc regarded 

 as primibrachs; while tliis term is convenient as indicating the ossicles of the 

 first di\isi.)n S(>ries, these are by no means always homologous, and therefore 

 the primibrachs of one species may be morphologically entirely different froni 

 the primibrachs of another (see figs. 1, p. 60, and 30, p. 71). 



Prismatic angles. — When the pinnules are prismatic, that is, triangidar in cross 

 section, as in the species of Calometridse, Thalassometridai and Charitome- 

 tridae, the median dorsal line becomes narrowed into a sharp gabel-hke ridge 

 and the ventrolateral borders become similarly sharpened; in a section of 

 such a puuiule the median dorsal hne and the ventrolateral borders stand 

 out prominently as three sharp angles which are laiown as the prismatic angles. 

 On the distal edges of the pinnulars it is at these angles, more particularly 

 the dorsal, that the production or overlap and the development of spines 

 reaches its maximum, and in many types in which the prismatic condition of 

 the pinnul(>s is but faintly indicated the great excess of spinosity at these 

 points shows the potential existence of prismatic angles (see fig. 54, p. SI). 



Prismatic pinnules. — Pinnules which are more or less sharply triangular in cross 

 section; they are characteristic of the families Thalassometrida?, Charitome- 

 trida?, and C'alometridie ; prismatic pinnules are associated with the presence 

 along the pinnule ambulacra of well-developed side and covering plates (see 

 figs. 49, 53, .54, p. 81, and 93, p. 153). 



Proximal. — See Distal. 



Proximal iorder. — Of the ccntrodorsal ; same as Inferior margin. 



Proximal cirrals. — The cirrus segments between the short outer segments which 

 bear dorsal processes and the short basal segments; this term is used in con- 

 trast to Distal or Outer cirrals. 



Proximal columnal. — The columnal inunediately beneath the calyx. 



In the comatulids this cohinnial separates from the one just beneath it 

 and increases enormously in size, becoming, wholly or in part, the centrodorsal. 



Proximal pinnules. — Same as Oral pinnules. 



Proximale. — In the post-palseozoic crinoids (excepting those belonging to the families 

 Encrinidse, and PlicatocrinidiB which are of the palseozoic type) the column 

 possesses a definite growth limit; wh(>n this is attained the topmost columnal 

 tj-pically enlarges, becoming permanently attached to the calyx by a close 



