98 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Postradial series. All the ossicles, collectively, which are borne by a single radial. 



Prebrachial stage. See Cystid stage. 



Primary anteroposterior axis. See Axis la. 



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



Primary cords. The five nerve trunks which arise from the central capsule (see 

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



Primary groove trunks. See Groove trunks 1 . 



Primary interradials. See Interradials 1 . 



Primary skeleton. The Badial skeleton, plus the centrale, the centrodorsal, or the 

 column. 



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

 post-radial axillary ; in case the arm does not divide all the brachials are regarded 

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

 first division series, these are by no means always homologous, and therefore 

 the primibrachs of one species may be morphologically entirely different from 

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



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

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

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

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

 such a pinnule the median dorsal line and the ventrolateral borders stand 

 out prominent!} 7 as three sharp angles which are known 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 pinnules is but faintly indicated the great excess of spinositj- 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 Thalassometridse, Charitome- 

 tridse, and Calometridae ; 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 border. Of the centrodorsal; 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 immediately beneath the calyx. 



In the comatulids this columnal 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. 



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

 Encrinidse, and Plicatocrinidse which are of the palaeozoic type) the column 

 possesses a definite growth limit; when this is attained the topmost columnal 

 typically enlarges, becoming permanently attached to the calyx by a close 



