l8 OPISTHOBRANCHIATA OF BRAZIL 



bands of strong muscle fibres. The body cavity is roomy, and 

 nearly filled by the viscera, its pseudo-peritoneum being colorless 

 or slightly yellowish in hue. 



Alimentary System. 



Pharyngeal bulb. The mouth communicates by a very short 

 tube with the pharyngeal bulb, a strong, muscular organ of conical 

 form. Its length is ii.o mm. with a maximum diameter of lo.o 

 mm. Opened from above the deep, rich amber-colored radula 

 is exposed, and in front of it, upon each side, the mandibular 

 plates of a similar color. The latter are situated at the anterior 

 end of the pharyngeal bulb, almost completely encircling the open- 

 ing and nearly touching each other above and below. The opales- 

 cent lip disc is elliptical in outline, the opening appearing as a 

 vertical slit, 4.0 mm. in length, while immediately within it the 

 margins of the mandibular plates are seen. These plates are 

 roughly rectangular in outline (PI. I, fig. 7), their length being 

 5.5 mm. and their breadth 3.0 mm. The posterior margin is 

 bounded by a sharp, regularly curved line of opalescent hue, 

 while the anterior margin is irregular, and more or less jagged 

 and worn. Each plate is made up of densely packed rodlets, 

 nearly straight, or slightly bent, and of approximately the same 

 diameter throughout their whole length. At the posterior mar- 

 gin of the plate the arrangement of these rodlets may be easily 

 seen (PI. Ill, fig. 12), but in the anterior portion such an arrange- 

 ment cannot be made out clearly, owing to the overlapping of 

 the rodlets as they increase in length. The shorter rodlets are 

 flattened antero-posteriorly, with a strong tendency to the forma- 

 tion of a slight concavity, or longitudinal groove upon the poste- 

 rior face, and a corresponding convexity in front. Their average, 

 greatest width is 0.005 ^"^- Toward the anterior border the 

 rodlets increase in length, their basal diameter remaining nearly 

 the same, while the length may reach 0.124 mm. The outer 

 extremity is bluntly rounded, the distal one-third being some- 

 times slightly enlarged, or club-shaped, or, in other cases, entirely 

 straight throughout (PI. Ill, fig. 13). The bending and dis- 

 tortion, incident to microscopic preparation as a whole mount, 

 indicate a considerable degree of flexibility. 



Radula. The radula is broad, deeply grooved behind, and of 



