548 A, E. Verrill— Catalogue of Marine Mollusca. 
Polycerella Emertoni Verrill. 
Polycerella Emertoni Verrill, Proc. U. 8. Nat. Mus., ili, p. 387, 1880. 
This species was first taken by me at Wood’s Holl, in September, 
1875, at the surface among eel-grass; and on hydroids from the piles 
of Long Wharf, New Haven, Conn., October, 1875. At Newport, 
R. 1, it was found by Mr. J. H. Emerton and the writer, in July and 
August, on filamentous alge, especially Ceramium rubrum and Des- 
merestia viridis, growing on the mooring buoys and piles of wharves 
in the harbor. In 1881, it was taken in considerable numbers in the 
harbor at Wood’s Holl, among eel-grass, in August and September. 
ap 
Idaliella pulchella Bergh. 
Idalia pulchella Alder and Hancock, Brit. Nud. Moll., part 6, fam. 1, pl. 17, figs. 
5-6. 
G. O. Sars, op. cit., p. 313, tab. 28, fig. 1, a—-c, tab. xiv, fig. 8, a-d (dentition), 1878. 
Verrill, Proc. Nat. Mus., ii, p. 198, 1879. 
Idaliella pulchella Bergh, Arch. fir Naturg., 47, i, [p. 7], 1881. 
PLATE XLII, FIGURE 13. 
This species was found, for the first time, upon the American 
coast, by Mr. J. H. Emerton, who discovered it at Salem, Mass., in 
1879. His specimens agree very closely with Sars’s description and 
figures, both in external characters and in dentition, but not so well 
with those of Alder and Hancock. 
Idaliella modesta Verrill. 
Idatia modesta Verrill, Amer. Journ. Sci., x, p. 41, pl. 3, fig. 3, July, 1875. 
Block Island Sound and north of Little Gull Island, in 17 to 40 
fathoms, 1874; Vineyard Sound and off No-Man’s-Land, 1875. 
Heterodoris Verrill and Emerton, gen. nov. 
Form and general appearance somewhat like Zriopa and Triopella, 
but stouter, and without any trace of gills. Mantle forming an edge 
all around the back; surface of the back with scattered papillz; a lon- 
gitudinal crest between and behind the dorsal tentacles, which are 
lamellose and retractile, without sheaths, but with a prominent 
fold of the mantle-margin in front of them. Head large, rounded, 
with ‘a free, thin margin, which has a flat tentacular lobe, on each 
side. Foot broad, rounded in front. A large opening, apparently 
the anus, on the right side between the mantle and the foot, behind 
the middle. Verge, as protruded, stout, cylindrical, swollen and 

