TETHYS-WEST AMERICAN. 85 



dd. Grayish-rose, each tentacle with a black line, 



lessoni. 



ddd. Not so marked ; slender, the tail long, robertsi. 



cc. Mantle with subcentral minute pore, posteriorly bilobed ; 



opaline gland with one orifice, panamensis. 



aa. Shell with an accessory plate near apex ; swimming lobes short, 



posterior, somewhat united behind ; excurrent siphon long, with 



a tongue-like lobe ; mantle with subcentral tube ; opaline gland 



with one orifice. Finely netted with brown and spotted with 



black, californica. 



T. NIGRA d'Orbigny. PI. 22, figs. 10, 11. 



Length as much as 25 cm. Body much elevated, leathery, 

 strongly wrinkled, very ventricose. Head short and wide, the neck 

 very short ; buccal lobes broad, quite short, a little folded at the 

 ends. Tentacles large, quite short, very obtuse and slit at the ends. 

 Foot very wide, strongly wrinkled, thick, truncated in front, 

 widened in the middle, short and subacuminate behind. Swimming 

 lobes not very large, united behind for a moiety of their length, and 

 forming a large branchial cavity ; in front the lobes are so short 

 that their free part can scarcely be of use in swimming. Mantle 

 very large, in part concealed by the union of the swimming lobes, 

 rounded, with a very small round aperture at the middle, above. 

 Posterior edge of mantle not having a tongue-like lobe, but excised 

 or sinused, and provided along the semicircle with a membranous 

 ridge, perpendicularly elevated, corresponding to the sinus of the 

 shell. Gill wholly covered by the mantle and by the bridge formed 

 by union of the swimming lobes. 



Color deep black, especially on the sole and lobes ; the latter a 

 little roseate inside. 



Shell very open, depressed, with- concentric and radial stria? ; 

 sinus wide and shallow ; apex a little oblique and slightly encrusted. 

 Amber colored. 



Island of San Lorenzo, Callao, Peru. 



A. nigra ORB., Voy. dans l'Ame>. Merid., p. 209, pi. 18, f. 1. 2. 



This species is remarkable for its large size, the union of the 

 swimming lobes behind, and the excised posterior margin of the 

 mantle, which is not produced to form an efferent canal as usual in 

 the genus. It emits a milky, white or slightly violaceous liquor in 

 abundance, and has a very strong odor of musk. 



