THE NAUTILUS. 141 



distance from the tip (Fig. 1). In many instances the presence 

 of an accessory branchia arising in this way is unaccompanied 

 by duplication of the pointed tips. 



The high sheath which surrounds the branchial rosette is 

 normally quite smooth. In only one of the many hundreds of 

 Chromodoris which I have handled was there noted any other 

 condition. In this single specimen, however, there were three 

 distinct ridges running from the dorsal surface to the external 

 margin of the branchial collar ; two of these ridges were ex- 

 tended in an anterior direction, their edges being sharp and 

 prominent, while the third, less conspicuously developed than 

 the other two, was on the left side of the collar. The appear- 

 ance of these structures is shown in Figure 2, where may be 

 seen the manner in which the ridges were united with the collar. 



The edge of the mantle occasionally shows evidence of injury, 

 and this may explain the origin of modifications found at the 

 anterior end of the mantle in several specimens. These modi- 

 fications consisted in a well-defined median indentation of the 

 buccal veil, which was thus symmetrically bilobed. But this 

 region of the mantle is almost always folded at the margin to 

 some extent, and since the pigment pattern frequently shows 

 no local disturbance at the region of the indentation, the feature 

 which is shown in Figure 3 (particularly at c) may be merely 

 an unusually strong expression of a tendency to wavy folding. 



The " rhinophores " of Chromodoris (cf. Arey, 1917), which 

 are usually straight, may appear somewhat bent near the tip, 

 or may even assume a slightly corkscrew shape. In one indi- 

 vidual there was found a bifurcating " rhinophore " on the left 

 side ; the one on the right side was normal. As shown in the 

 accompanying sketch (Fig. 4), the rhinophoral collar (c) had 

 grown in such a manner as to accommodate the additional 

 structure. 



One specimen occurring among a lot of 231 collected early in 

 January, 1917, was found to possess a striking modification of 

 the rhinophoral collars. Figure 5 depicts the condition refer- 

 red to, which consists in the fusion of the two pockets, into 

 which the " rhinophores " are respectively retracted, so that 

 but a single depression provided with a single collar is present 



