676 PROCEEDINGS OF THE NATIONAL MUSEUM vol.xxiii. 



furrow or slit is siiort and narrow, and, judging" from the appearance 

 of the specimens, where the beak of the valve is })roken away it opened 

 into a pedicle chamber that was closed at the outer end as in OhoJellu 

 crassa and other species of the genus. On the dorsal valve there is no 

 evidence of a true area except in the presence of a narrow, thickened 

 rim somewhat like that of the dorsal valve of B'tchi (jemma. None of 

 the muscle scars are shown in the ventral valve. The position of the 

 central and anterior lateral scars of the dorsal valve is indicated b}" 

 the outline of the visceral cavity. Of the vascular markings the main 

 sinuses are clearly shown in each valve, also the outline of the position 

 of the parietal scar. 



Ohservatlons. — This beautiful little shell has remained without illus- 

 tration since Dr. Linnarsson gave it a name in 1809, based on the 

 "singular sculpture'' of the outer shell. In a collection made for me 

 by M. Schmalensee, the collector of the Swedish Geological Surve}', 

 there were several specimens showing casts of the interior more or 

 less imperfectl3\ From these I was able to ascertain that the shell 

 had the generic characters of Obolella, although differing from the 

 typical species of that genus in the character of the surface ornamen- 

 tation. The outer surface has been seen onl}^ on the posterior umbonal 

 portion of the valves in the shells collected for me by M. Schmalensee. 



Formation and locality. — Lower Cambrian. Fucoid sandstone. 

 Vestergotland, Bithingen, Sweden. 



Genus BICIA, we^rv genus. 



Shell subequivalve, moderately convex; longitudinallv ovate, with 

 the ventral valve sometimes subacuminate and the dorsal valve sub- 

 circular. Beaks of both valves as now known terminate at the poste- 

 rior margin. Surface marked by concentric and radiating aivvx. 



Shell substance unknown in an unaltered condition. Shell structure 

 formed of a thin surface layer and numerous inner layers or lamellte 

 more or less oblique to the outer layer. Area of the ventral valve 

 usually on the plane of the edges of the valve, but in some instances 

 rising at a low angle; it is usually high, and triangular in outline, but 

 the apex may be I'ounded and the base curved forward at the median 

 line; divided midway by a narrow pedicle furrow and again at each 

 side by a narrow flexure line that extends forward and outward from 

 the apex. Area of dorsal valve short, appearing in both of the known 

 species to rise from the plane of the edges of the valve. Strife of 

 growth subparallel to the base cross the areas. 



The main vascular sinuses of the ventral valve are narrow and 

 extend forward from the projecting center of the base of the area, 

 gradually separating as they cross the visceral area and extending for- 

 ward beyond the transverse center of the shell; in the dorsal valve 

 they appear to separate more rapidly and to follow the outer margin 



I 



