MARINE MOLLUSCA OF THE UNITED STATES. 111 
Genus POLYCERA, Cuvier. 
Regn. Anim. If. 390, 1817. 
Animal smooth or tuberculated ; tentacles clubbed and pecti- 
nated, not retractile, and without sheaths; frontal veil consisting 
of a series of tentaculiform appendages variable in number, often 
extending along the borders of the mantle; branchie forming 
part of a circle around the vent, encased by membranous laminz 
which protect them. ; 
ier. Lussonmy, Orb. Fig. 227. 
Mag. de Zool., vii. 5, t. 105. 
Polycera citrina, Alder, Ann. Nat. Hist., vi. 804, t. 9, f. 1-9. 1841. 
Polycera modesta, Lovén, Index Moll. Greenl., 6. 1846. 
Doris tlluminata, Gould, Invert. Mass., edit. i. 4. 1841. 
fassuchusetts; North Europe. 
Family TRIOPID A. 
In this family the body is somewhat angular, and the mantle is 
distinct and furnished with tubercular appendages; the species 
of the genera comprising this group constitute some of the most 
delicate and beautiful forms of nudibranchiate mollusks. 
Genus ANCULA, Lovén. 
Ind. Moll. Scand., 5. 1846. 
Body slender, with clavate processes bordering the branchial 
region of the back ; tentacles clavate, perfoliate, laminated, armed 
at the base with styliform appendages. 
1. A SULPHUREA, Stimpson. Fig. 228. 
Invert. Grand Manan, 26. 1853. 
Body long, slender, light-brownish; branchial plumes three, 
arranged in a semicircle, anterior largest, doubly pinnate; sur- 
rounding tentacular processes eight to twelve, sulphur-tipped ; 
oral tentacles long, the processes arising from their very base. 
Length 30 mill. 
Family TRITONIID A. 
Many of the genera of this family are pelagic, and are often 
found crawling on the fronds of floating alge or clinging to the 
narrow stems of gulf-weed, which is frequently met with in large 
masses at considerable distance from the land; these mimic forests- 
