160 RAYMOND C. OSBURN AND RUTH M. VETH Vol. XXII, No. 6 



structure consists of four mamillate, or low, rounded-conical 

 structures, which are heavily chitinized, provided with pointed 

 chitinous teeth of varying length and thickness and which are 

 continuous with the chitinous cone. The arrangement of these 

 cones, with their bases directed outward, gives a somewhat 

 squared outline to the gizzard in cross-section, as shown in 

 PI. I, Fig. 3. The rounded surfaces, with the teeth pro- 

 jecting into the lumen of the digestive tract, practically close 

 the cavity when the gizzard muscles are contracted, and the 

 teeth are interdigitated when in this position. In operation in 

 the living specimen, the gizzard lobes are seen to separate for 

 some distance and then to close strongly and sharply together. 



While in Bowerba?ikia and related genera each epithelial cell 

 of the gizzard is chitinized on its grinding surface (see Fig. 8), 

 thus making as many teeth as there are cells, in Buskia this is 

 not the case. The hollow concavity of the chitinous cone is 

 filled with elongated epithelial cells, those nearest the center 

 being the longest. Together these cells secrete the chitinous 

 lobe as one continuous structure, the teeth also being a part 

 of the mass (Figures 3 to 7). 



With its band of muscles, the entire gizzard in Buskia 

 armata measures only about .075 mm. in diameter. Each cone 

 measures about .0414 across the base and about .0234 in height. 

 The teeth are quite variable in size but average about .007 mm. 

 in height. Each cone bears about 30 teeth, though often the 

 number is much less than this, and the teeth at the tip of the 

 cone are larger and stronger than those farther down on the 

 side. The layer of chitin is about .002 mm. in thickness, when 

 fully developed, but thins out somewhat toward the base and 

 then suddenly becomes thickened at the margin to form a ring 

 about the base. The teeth are conical and hollow at the base 

 and the chitin forming them is somewhat thicker than that of 

 the cone on which they are borne. These relations are well 

 shown in Figures 3 to 7. 



Much variation is shown in both sections and total mounts 

 in the exact form of the chitinous cones, possibly depending 

 somewhat upon the amount of chitinization. Sometimes the 

 lobes are almost hemispherical and seem to lack the rim around 

 the base. As such structures appear thinner and lighter in 

 color, it is probable that they have not reached their full devel- 



