106 BULLETIN 82, UNITED STATES NATIONAL MUSEUM. 



Tnangular processes. — The iiiterrndial j)rocesses of tho rosette (see figs. 577, 578, 

 pi. 10, and 589, 590, pi. 14, ami pp. 320-322;). 



Tripled dorsal spines. — Dorsal spmcs which occur, three on each cirral, in a line ut 

 right angles to the lojigitudLaal axis of the cirrus (see fig. 348, p. 289). 



Trivium. — In species of comasterids jjossessing ungroovcd arms and primary bilat- 

 eral symmetry, the three anterior arms; that is, the anterior, tho right anterior, 

 and the left anterior arms (see pp. 110, 111); (see Bivium, Axis, and Orientation) . 



TrocJiitse. — Fossil columnars, considered individually. 



U. 

 Underbasals. — See Infraiasals. 

 Ungrooved arms. — See Grooveless arms. 

 Unplated ambulacra. — Ambulacra bordered by rudimentary side and coTering 



plates not visible on ordinar}' examination, or by none at all. 

 Unplated disk. — A disk upon which no epidermal calcareous plates are to be found 



on ordinary examination (see figs. 15-17, p. 67). 

 Upper surface. — The surface of tho animal, or the surface of any part of the animal, 

 which is directed awaj- from the ground or the base when the animal is in 

 its natural position. 



Thus the ventral surface of the animal as a whole is the upper surface. 

 Of the centrodorsal and the cirri, or tho stem, or of their component parts, 

 the proximal surface or surfaces are the upper, but of the other elements 

 the distal. 



V. 



Ventral interradlal furrows. — The furrows on the ventral surface of the radial 



pentagon which lie over the intcrradial sutures (see figs. 453, p. 355, 464, p. 357, 



465-467, p. 359, 477, 478, p. 363, 488, 489, p. 365, 497, 499, 500, 501, p. 369, 



503, 505, 507, 508, p. 371, and 509-511, p. 373, and p. 374). 

 Ventral margin. — Of the centrodorsal (see Inferior margin) . 

 Ventral perisome. — The perisome of the disk and of the ventral surface of the arms 



and pinnules. 

 Ventral spines. — On the cirri; long overlapping spines sometimes developed on the 



distal midventral margin of the earlier segments. 



Ventral spines are xerj rare, but are well developed in the species of the 



genus Pteronietra. 

 Ventral surface. — See Adoral. Of the centrodorsal, tliat surface which is in contact 



with the radials (see figs. 229-234, p. 247). 

 Ventrolateral processes. — The produced ventrolateral borders of the ossicles of the 



division series and of tho first two brachials, as seen in Stephanometra and 



Cenometra (see fig. 87, p. 143). 

 Visceral mass. — The central capsule resting upon the radials and tho arm bases 



and bounded ventrally by the disk and laterally by tho division series and 



so-called interradial areas. 



