62 OPISTHOBRANCHIATA OF BRAZIL 



Radula. The radula is nearly colorless, about one and one- 

 half times as long as broad. The rhachis is narrow and naked, 

 the lateral teeth are tmciform, strongly hooked, and arranged 

 in 48 rows, with from 42 to 50 teeth in each half row. The dental 

 formula may hence be expressed as 42-50 :o :42-5ox48. The inner- 

 most tooth in each row (PI. XI, fig. 52) is somewhat smaller 

 than its neighbors, the remaining teeth being approximately of 

 the same size, with the exception of the outermost ones, which 

 decrease gradually in size, the last ones of the series becoming 

 flattened and almost rudimentary (PI. XI, fig. 49). The body of 

 each tooth (PI. XI, figs. 50-52) is oblong, flattened, slightly 

 oblique, its posterior end truncate, in some cases emarginate or 

 notched. The anterior end is rounded, the inner margin expanded 

 into a flattened wing, which is overlapped by the next inner 

 tooth, the outer margin being nearly straight. Viewed from below 

 (PI. XI, fig. 53) the bases are of a somewhat oval outline, becom- 

 ing more linear toward the ends of the rows. A typical tooth, 

 such as the one shown in side view in PI. XI, fig. 50? taken from 

 the middle of the 22d row, measures 0.025 mm. in total length 

 of base, the height of the hook above the bottom of the base is 

 0.014 mm. The outermost tooth, such as is shown in fig. 49, of 

 PI. XI, taken from the nth row, is o.oi mm. in base length, its 

 total height being 0.006 mm. 



Viscera. The very poor preservation of the viscera pre- 

 cluded any satisfactory study of their structure and relations, 

 their hard and brittle condition resisting all attempts at softening. 



NERVOUS SYSTEM. 



Central ganglia. The central nervous system is enveloped 

 in a closely fitting connective tissue capsule, very difficult to 

 remove, which also binds it closely to the buccal mass. The 

 cerebro-pleural complex (PI. XII, fig. 55) is closely fused, and the 

 two sides are in such close contact in the median line that no 

 commissures connecting them may be made out. No distinct 

 line of demarcation can be made out between the cerebral and 

 pleural moieties of the complex upon either side, nor is there any 

 grouping of the nerve cells to correspond to such a division. 

 The separation into two distinct ganglia as shown by Von 

 Ihering ('77) for PL meckeli (fig. 8, Taf. II), does not here 



