Fam. 43.] NATUKAL HISTOKY SOCIETY. 121 



oral tentacles ; gills simply pinnate, set in an open circle or 

 ellipse, non-retractile. 



* Gill plumes over 15.. 1. 



" Gill plumes only 5 2. 



* Gill plumes 6-10 3, 4. 



1. Onchidoris bilamcUnta, L. Animal oblong-elliptical; surface 

 covered with unequal, short, pestle-shaped papillse ; gills slender, 

 simply pinnate, 20-25 in number, arranged in an oval across the 

 back; several tubercles within the included space, Whitish, 

 varied with rusty brown, or flesh color. L. 25 ; W. 12. — New 

 England. 



2. Onchidoris grisea, Stini. Body oval-oblong, quite convex, 

 and semi-globose when contracted; a little pointed behind when 

 fully extended ; back covered with short, blunt processes tipped 

 with stellate clusters of spiculse ; gills forming a star of 5 short, 

 yellowish plumes, around a brown spot with a dark bristle in 

 the centre ; back plumes much shorter than the front ones ; head 

 short, broad, angular. L. 12 ; W, 8. — Mass. 



3. Onchidoris tenella. Ag. Body ovate, broadest in front ; man- 

 tle extending in front much beyond the foot, on the sides but lit- 

 tle ; gills forming a star of 6 to 7, simple, short plumes, retractile 

 into separate sheaths ; foot elliptical-oblong ; head short, broader 

 than foot, pointed at the sides, broadly shielded by the mantle. 

 Yellowish-white. L. 13 ; W. 10.— Mass. 



4. Onchidoris aspersa, A. and H. Body oblong-elliptical, 

 covered with large, mushroom-like tubercles ; gill star of 7 or 8 

 broad, lanceolate plumes, retractile into separate sheaths ; head 

 short, crescentic, about as wide as the foot which is a little nar- 

 rower than the manlle. Pale cream color, the tubercles lighter, 

 a dusky spot in the centre of the back. L. 12 ; W. 6 — Mass. 



3. AcANTHODORis, Gray. 



Body convex ; mantle moderate in size, covered with soft pa- 

 pillae ; oral tentacles united in a veil, with free, flattened, lateral 

 ends ; gills united at the base, non-retractile. 



1. Acanthodoris ornata, Ver. Body elongated, high at the sides, 

 somewhat oblong, narruvvci and rounded behind, extending 

 much beyond the mantle ; mantle narrowed in the middle and 

 covered with small papillae, except along the centre ; lower half 

 of the slender dorsal tentacles smooth, upper half with about 16 



