MARINE MOLLUSCA OF THE UNITED STATES. Ill 



Genus POLYCERA, Cuvier. 

 Regn. Anim. II. 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 ; branchiae forming 

 part of a circle around the vent, encased by membranous laminae 

 which protect them. 



1. P. Lessonii, Orb. Fig. 227. 



Mag. de Zool., vii. 5, t. 105. 

 Polycera citrina, Alder, Ann. Nat. Hist., vi. 304, t. 9, f. 1-9. 1841. 

 Polycera modesta, Loven, Index Moll. Grcenl., 6. 1846. 

 Doris illuminata, Gould, Invert. Mass., edit. i. 4. 1841. 



Massachusetts ; North Europe. 



Family TRIOPID^E. 



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 ANCTJLA, Iioven. 

 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^E. 



Many of the genera of this family are pelagic, and are often 

 found crawling on the fronds of floating algse 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- 



