PLATE 4. 



Fig. 1-3. DOLABELLA AGASSIZI, Sp. nOV. 



Fig. 1. Detail of the distribution of the osphradio-ctenidial nerve as seen from below; au, 

 auricle; v, ventricle; c. a, crista aortae; ao, aorta; ;>. a, visceral artery; g. a, gastric artery; g, 

 genital artery; p. h, dotted line indicating the boundary of the pericardium; o. B, dotted line indi- 

 cating the boundary of the organ of Bohadsch; s. h, dotted line indicating the boundary of the shell; 

 r-p. 0, reno-pericardial opening. The parieto-visceral ganglion complex lies above the main aortic 

 tnmk at the top of the figure, the left visceral ganglionic moiety lying in front of the right parietal por- 

 tion. At their left anterior ends they are joined by their respective connectives from the pleural gangUa 

 (Plate 2, fig. 1, pl-i'. con, pl-par. con); v. 2, the second visceral nerve, branching at once into r. 2a and 

 V. 2h, which are distributed (Plate 3, fig. 2); p. 1, first parietal, or vulvar nerve; p. 2, second parietal, 

 or osphradio-ctenidial nerve. The main branches of this nerve are numbered in series; 1 to peri- 

 toneum; 2 to the raiddorsal peritoneum and the integument forward, giving off a branch 2a, which 

 anastomoses with a twig from the seventh pedal nerve, 7 p. The branch 3 bifurcates into .5 and 6, the 

 first passing to the anterior portion of the mantle, while the second passes to the outer face of the kidney, 

 giving off the branch 7 to its ventral face on the way. The main trunk, 4, now thickens decidedly and 

 gives off S and 9 to the venous sinus at the base of the heart and to the mantle. Numerous minute 

 short branches pass to the osphradium, asp., shown here in outline. The branch 10 ramifies to the 

 wall of the brancliial chamber above the ctenidium, and to the walls of the branchial sinus at its base. 

 The main trunk, 11, now enters the ctenidium, ct, shown here in outline, and continues as the chief 

 ctenidial nerve ct. n, to its tip, giving off numerous fine branches on the way. No distinct osphradial 

 nor branchial ganglia other than represented in the thickened nerve-trunk itself are to be found. X 2. 



Fig. 2. Ventral view of shell. X 1.7. 



Fig. 3. Detail of common genital opening. The anterior end is directed toward the upper 

 side of the figure; a, the integumental fold continued forward from the region of the siphon, as 

 shown at g, (Plate 6, fig. 1), along the floor of the palhal ca\'ity and forming the dorsal margin 

 of the genital opening. From its anterior curvature the dorsal or left ridge, I, of the genital furrow 

 extends forward, approaching its fellow, r, of the right side, which is a continuation of the incomplete 

 septum partially dividing the common genital opening into a dorsal and a ventral portion. X 3. 



