PLATE 6. 



Fig. 1-9. DOLABELLA AGASSIZI, sp. DOV. 



Fig. 1. Diagram showing the relations of the pallial organs; a, inner boundary of base of parapodia; 

 h, projection of outline of posterior body-disc upon underlying organs; k, similar projection of the upper 

 margin of parapodia, continuous in front as a low ridge; c, outline of boundary of shell; d, right margin 

 of mantle, extending from between the anterior ends of the parapodial lobes backward, its posterior 

 margin refiexed dorsally at e, thence continued transversely and rising into the siphon margin at s; 

 at the posterior edge of the siphon base it becomes nearly indistinguishable, but may be followed as 

 a faint elevation to the right behind the anal opening, /, thence merging into a strong fold, g, which 

 curves forward along the floor of the pallial chamber to the reproductive opening, h, where it is con- 

 tinued around as its front margin and disappears within it (c/. Plate 4, fig. 3) ; i, genital furrow, extend- 

 ing forward from the genital opening, h; I, margin of the shell-foramen; n, cushion-Uke prominence at 

 bottom of siphon. Natural size. 



Fig. 2. Typical lateral tooth from posterior region of radula in side view, a-h, base; c, tip of 

 hook. X 100. 



Fig. 3. Median tooth from 12th row of radula, in face view. No indication of a hook, it being 

 worn away probably. X 175. 



Fig. 4. Median tooth from 13th row of radula. X 175. 



Fig. 5. Diagram of the palUal cavity; the mantle being cut away along the double line m, expos- 

 ing the underlying ctenidium; a, outline of inner boundary of base of parapodia; /c, projection of free 

 upper margin of parapodia upon the underlying organs continuous in front beyond the pallial cavity; 

 6, outUne of projection of the margin of the posterior body-disc; m, cut edge of mantle, tlie incision 

 being carried around close to the origin of the left attached margin of the mantle from the body-wall, 

 thus laying open nearly the whole extent of the upper gill-cavity, except at the left posterior margin, 

 where it reaches shghtly farther back; of, afferent blood-vessel to ctenidium, ej, efferent blood-vessel 

 to the same. That portion of the ctenidium lying to the right of a hne joining af and ef projects freely 

 into the paUial cavity, that to the left of the same is attached along its margin to the body-waU; h, 

 common genital opening, its borders leading forward as the dotted lines to continue as the external sper- 

 matic groove, I, to the right side of the head; s, siphon; c, the cushion-like prominence at the base of the 

 siphon, directly below the posterior rounded opening between the parapodia; o, osphradium. Natu- 

 ral size. 



Fig. 6. MecUan tooth from 20th. row of radula in side view. A sUght median hook present, but 

 is worn; the anterior end of the thick basal portion is curved upward. X 175. 



Fig. 7. Median tooth from 23rd. row of radula in face view. X 175. 



Fig. 8. Median tooth from 31st. row of radula in side view. X 175. 



Fig. 9. Median tooth from 59th. row of radula in side view. The hook here reaches its greatest 

 development. X 175. 



