308 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



sinus below which, in a loop of the pleurocyst, is a large, external, 

 pear-shaped frontal avicularium. The avicularium is mounted on a 

 mound of varying prominence and outlined by a line leading to the 

 peristomial notch. A few frontal pores, spaced far apart, encircle 

 the avicularial mound. Primary orifice with low wide lyrula and two 

 large, blunt cardelles. Ovicells globose, with a few pores outlining 

 the frontal area. Mandibular area large and oval. 



This species is named for the decorative effect of its frontal 

 avicularium, from the Latin "ornatus" (decorated, adorned) and 

 "pectoris" (chest). 



Measurements: Minimum to maximum and average measure- 

 ments, in millimeters, are given below (for explanation see p. 271). 



Z-L, 1.427-2.001 (1.696) S^Or-W, 0.259-0.317 (0.280) • 



Z-W, 0.522-0.999 (0.745) Se-Or-Si-D, 0.072-0.115 (0.092) 



Av-L, 0.331-0.461 (0.400) Se-Or-Si-W, 0.058-0.101 (0.073 mm.) 



Av-W, 0.202-0.274 (0.232) Ly-L, 0.029-0.043 (0.031) 



B-L, 0.259-0.317 (0.294) Ly-W, 0.079-0.101 (0.090) 



Pr-Or-L, 0.230 (Two readings) Ov-L, 0.547-0.562 (Three intact ovi- 

 Pi--Or-W, 0.259 (Two readings) cells) 



Se-Or-L, 0.187-0.259 (0.222, excluding Ov-W, 0.504-0.547 (Three intact ovi- 

 sinus) cells) 



Zoarium: The zoarium is encrusting and of ivory color. It is 1' 

 brittle and fragments easily. 



Zooecia: a salient rim outlines zooecial boundaries. Zooecia are ) 

 very large, considerably longer than wide, and 4-6-sided. Two kinds s 

 are present, those with ovicells and those without. The latter are in 

 the majority. The frontal wall is gently convex except in a few zooecia 

 where the avicularial mound develops into an excessive bulge (pi. 

 33,F). The frontal is a pleurocyst, with areolae, short interareolar 

 ribs, a pebbled surface, and a few small widely spaced pores around 

 the avicularial mound. The areolar pores are large and close together. 

 Some zooecia have a smooth rather than a pebbled surface. The 

 lateral walls are thinner. A line of rounded pores (sometimes as 

 many as 10) of fairly uniform size and equal spacing can be seen in the 

 lateral walls. 



Avicularium: A single avicularium is present on each zooecium, 

 with position and orientation identical in all cases. The avicularium 

 is cradled on a mound in the midline just proximal to the peristomial 

 notch. The pleurocyst forms a loop around it and continues distally 

 on each side beyond it to form the peristome (pi. 33, A). The 

 avicularium is large and pear shaped. Its small, subcircular distal 

 part is called the "back area." Its shallow, wide, oval, large, proximal 

 part is the "beak, rostrum or mandibular area." A short pivot bar 

 separates the two across the top. The avicularium is longitudinally 

 placed and occupies a considerable part of the frontal surface. It lies 



