184 MEGATEBENNUS. 



Dr. Dall's original description is given. The external anatomy- 

 is described by him in the place cited above. The epipodial line 

 has papilla?, according to him ; so it is likely that my specimen was 

 deficient or imperfect, perhaps from too long remaining in alcohol. 

 It is described above. 



Section Amblychilepas Pilsbry, 1890. 



Large-fissured Fissurellida? with a saddle-shaped shell, elevated 

 at the two ends, its margin thickened, blunt, not crenulated and 

 without a white border or rim above. The perforation oblong or 

 oval, subcentral. Type F. trapezina Sowb. 



The animal is not known. The excessively unsatisfactorily con- 

 dition of our knowledge of the animals of the Fissurellidse renders 

 systematic work with the shells alone very uncertain. It has seemed 

 to me necessary to institute this group in order to have a place for 

 the following oriental species, which have a somewhat different 

 aspect from the West American Megatebennus. 



M. scidellum Gmel. (hiantula auct. not of Lam.) is probably 

 equally typical of the group with the trapezina. 



From Clypidella the shells of this genus are separated by the 

 much wider, subcentral (not anterior) orifice, non-crenulated mar- 

 gin, etc. 



M. scutellum Gmelin. PL 39, fig. 89 ; pi. 44, figs. 99, 100, 1, 2. 



Shell oblong-oval, low-conical, compressed at the sides ; perforation 

 a little in front of the middle, rather large, oval, about one-fifth the 

 length of the shell. Color grayish, with broad rays of purple or 

 red. 



The outline is oblong ; in front and back more or less convex, 

 compressed and flattened along the sides. The margin at both ends 

 is strongly raised, so that when placed on a plane the sides alone, 

 support it. It is sculptured with very numerous close radiating rib- 

 lets, subobsolete concentric growth-lines, and generally has the posi- 

 tions of one or two former peristomes marked by slight ledges. In- 

 side white or nearly so, having a rather wide callus margin around 

 the perforation. Muscle-scar deeply impressed, very near the edge, 

 its anterior extremities connected by a deep, curved muscle-impres- 

 sion. Margin blunt, not crenulated. 



Length 34, width 21, alt. 10 mill. 



Cape of Good Hope. 



