CAMjENA-OBBA. 107 



having a strong fold within the outer Up, marked outxide by a deep 

 pit, as in Cepoli*. Type C. merarcha, pi. 39, figs. 9, 10. 



Anatomy unknown. The two species are from Tonquin. The 

 relations of the group are problematical, but judging from shell 

 characters, it belongs near either Obba or Camcenel/<i. 



C. merarcha Mab., vi, 235. C. morleti Dautz. & d'Ham., vi, 240. 



mercatorina Mab., vi, 121. 



Genus OBBA Beck, 1837. 



Obb<t BECK, Index Moll. p. 30 (proposed for H. planulata, papilla, 

 mamilla}. GRAY, P. Z. S. 1847, p. 172 (H. planulata selected as 

 the type). See also PILSBRY, Manual of Conch, vi, p. 211, and 

 viii, p. 270. Gallina HARTM., Erd u. Siisswasser Gast. Schweiz, 

 1840, p. 197 (H. rota Sowb.). Philina (in part) ALBERS, Die Hel. 

 1850, p. 119 (preoc.). Pusiodon SWAINS., in part. Obbina SEM- 

 PER, Reiseu im Archip. Phil., Landmoll., ii, p. 123 (type H. planu- 

 lata'), 1873. 



Shell varying from trochoidal to depressed lens-shaped ; carinated, 

 at least in the young; umbilicated ; the surface striated or wrinkled 

 in the direction of f/roivth-lines. Nucleus composed of about two 

 polished whorls, not distinctly marked off from the after growth. 

 La*t whorl very deeply deflexed in front, aperture subhorizontal ; ends 

 of the expanded perittome approaching, and connected by a cord or 

 raised callus ; basal lip reflexed and often bearing a tooth. Whit- 

 ish, buff or light brown, banded or speckled with brown. Type 0. 

 plnmlata, pi. 19, figs. 14, 15, 16. (See also pi. 19, fig. 17, 0. basi- 

 dentata). 



Animal having a very broad flat foot, the tail short and quite flat, 

 sole undivided ; tentacles short (pi. 39, fig. 7, 0. planulata}. 



Jaw smooth, without median projection, or with it small and blunt. 

 Dentition : Central and inner lateral teeth having wide mesocones, 

 no side cusps. Marginals developing a bifid mesocone and an ecto- 

 cone, the outer marginals having both mesocone and ectocoue split 

 showing four short cusps, as in Camiene/fa ptatyodon. (PI. 39, fig 

 8, central and marginal teeth of 0. planulata ; pi. 39, fig. 6, an 

 inner marginal of 0. baddentatu^). 



Genitalia lacking accessory appendages on the female side, the duct 

 of the spermatheca short. Penis short, continued in a longepiphallus 

 bearing the retractor muscle, vas deferens and a flagellum. The 



