268 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



Zooecia: Approximate external zooecial length measurements, from 

 orifice to succeeding orifice: 1.296-1.728 mm. (average 1.492 mm.). 

 The zooecial front is somewhat bracket-shaped (pi. 18,A,B). Im- 

 mediately below the orifice the two mucros jut out with their cradled 

 external avicularium to form a broad, irregular shelf in front of and 

 below the orifice (pi. 18,C-E). From there on downward (proximally) 

 the zooecial frontal slopes gradually inward toward the orifice of the 

 zooecium below (pi. 18,A). The front wall is much thicker than the 

 side or back walls. The process of zooecial development and calcifi- 

 cation can best be observed in the incomplete, forming zooecia at the 

 tip of the colony (pi. 18,B). The thin, smooth, innermost calcareous 

 layer forming the front of the zooecium is the olocyst. Over it, 

 beginning around the areolar pores, spreads the channeled porous 

 tremocyst whose thickness increases with age. The number of pores 

 is considerably reduced over the ovicell. Thus, it is possible to recog- 

 nize ovicelled zoids from sterile ones. A few zoids developed chitinous 

 rootlets (pi. 18,F,G). 



Avicularia: Each zoid has an internal and an external avicularium. 

 Occasionally a zoid will show two instead of one external avicularium 

 (pi. 18, G). The base or back area of the external avicularium is on 

 or near the midline. The beak rests against the inner side of one of 

 the mucros. This points it obliquely forward and somewhat distally. 

 The placement of the external avicularium therefore ranges from 

 transverse to a slight oblique distal inclination that sometimes amounts 

 to a 30° or 40° angle. Measurements from the external avicularia: 

 total length 0.144-0.230 mm. (average 0.189 mm.); total width 

 0.101-0.144 mm. (average 0.118 mm.); mandible length 0.101-0.130 

 mm. (average 0.112 mm.); mandible width 0.086-0.101 mm. (average 

 0.097 mm.); beak length 0.115-0.158 mm. (average 0.140 mm.). 



The internal avicularium is placed obliquely below and to the side 

 of a corner of the orifice (pi. 18,C-E). The tip of its strongly hooked 

 beak is just barely visible from the outside and points upward and 

 outward, somewhat. The internal avicularial mandible is triangular, 

 strongly hooked, and chitinized (pi. 18,1). The external avicularial 

 mandible is a bit more rounded at the tip and only slightly hooked 

 (pi. 18, H). Measurements for internal avicularia: beak length 0.144 

 mm.; mandible length 0.086-0.130 mm. (average 0.115 mm.), width 

 0.072-0.122 mm. (average 0.103 mm.). Beak length and mandible 

 width are from only three readings, mandible length from six. 



Frontal oral ledge: A thin, long rim acts as the oral ledge in this 

 species. It extends from the side of the inner avicularium to the 

 opposite side of the orifice (see pi. 18,C-E). It is so thin and narrow 

 that it could easily be overlooked. 



