266 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 1 05 



the back wall to the outside frontal surface), 0.763-1.109 mm. (average 

 0.933 mm.). 



The zooecial walls are as in other species of the genus (pi. 17,C,F). 

 The back wall has occasional small pores, very few in number. The 

 side wall has rosette plates, and a couple of rows of single pores at 

 its frontal border. Side wall 0.007-0.014 mm. (average 0.010 mm.) 

 thick. Channeled frontal wall 0.144-0.446 mm. (average 0.301 mm.) 

 thick; its frontal pores irregular and 0.029-0.079 mm. (average 0.055 

 mm.) in diameter. 



Avicularia: An internal avicularium is obliquely placed to one 

 side of the orifice high enough for the tip of its hooked beak to show 

 a little from the outside (pi. 17, A-G). In fact, it is almost vertical 

 in orientation. Dimensions: total length 0.187-0.288 mm. (average 

 0.247 mm.); total width 0.122-0.158 mm. (average 0.142 mm.); 

 beak length 0.115-0.187 mm. (average 0.157 mm.); mandible length 

 0.115-0.144 mm. (average 0.126 mm.), width 0.108-0.130 mm. 

 (average 0.107 mm.). 



A sharply pointed external avicularium, transversely placed, is 

 cradled between two mucros. Its back area is usually on or near 

 the imaginary midline which passes through the orifice. Its bent 

 and hooked beak rests against one of the mucros (pi. 17,A,E,II), 

 which is farther away from the midline than the "naked" mucro, 

 which is very near or in front of the corner of the orifice. An occa- 

 sional zoid has two external avicularia (pi. 17, G) with a mucro be- 

 tween them. Likewise, a rare zoid may lack the external avicularium. 

 Measurements for external avicularia: total length 0.187-0.259 mm. 

 (average 0.233 mm.); total width 0.115-0.202 mm. (average 0.159 

 mm.); beak length 0.130-0.158 mm. (average 0.144 mm.); mandible 

 length 0.101-0.130 mm. (average 0.114 mm.); mandible width 0.115- 

 0.173 mm. (average 0.134 mm.). 



Frontal oral ledge. The frontal oral ledge cuts diagonally 

 outward across the floor of the primary orifice (pis. 17,A-C,E-G). 

 Its plane is at a considerable angle to the plane of the internal avicu- 

 larium. However, this angle is not as great as in C. rossi (see pi. 

 13,E,K) but is greater than in the other four species of the collection. 



Orifice: The orifice is arched distally and a bit lopsided rather 

 than a perfect semicircle. Also, to add to the distortion, the curved 

 oral ledge gives the orifice a crescentic shape and makes it appear set 

 somewhat obliquely into the frontal surface (pi. 17,A,B). A shallow 

 groove appears between the internal avicularium (pi. 17,F) and the 

 oral ledge, outward. The primary orifice is 0.202-0.288 mm. (average 

 0.243 mm.) long and 0.267-0.389 mm. (average 0.332 mm.) wide. 

 The secondary orifice is a bit larger: length 0.245-0.317 mm. (average 



