148 FISSURELLA. 



F. COSTATA Lesson. PL 30, fig. 10 ; pi. 35, fig. 11, 



Shell depressed, rounded-oval, apex a trifle in front of the center ; 

 having radiating riblets ; perforation small, oblong, twice as long as 

 wide, one-thirteenth to one-fifteenth the length of the shell, and hav- 

 ing a tendency to develop two little projections or teeth on each 

 side. 



The shell is very like F. lata, but is more depressed more nearly 

 circular, and the hole is smaller. It is ashen grayish, rayed rather 

 obscurely with olive-brown. 



Length 74, width 63, alt. 27 mill. 



Length 67, width 55, alt. 17 mill. 



Valparaiso, Chili. 



F. costata LESSON, Voy. de la Coquille p. 410, 1830 ; Illust. Zool., 

 t. 12. REEVE, Conch. Icon., f. 14. SOWB. Thes. Conch, iii, p. 

 187, f. 15, 205. F. chilensis SOWB. Conch. Illust., f. 36. F. rudis 

 DESK., teste Reeve & Sowerby. 



More rounded than usual, and with an exceptionally small foramen. 

 Specimens of very depressed form occur, the flattest I have seen 

 measuring, length 49, breadth 39, alt. 10 mill. ; the altitude 

 being a trifle over one-fifth of the length, while in the more typical 

 examples the height is contained about three times in the length. 



F. POLYGONA Sowerby. PI. 60, fig. 84. 



Oval, angulate, anteriorly narrowed, white, interruptedly rayed 

 with purple ; with numerous scabrous striae and fewer cateniform 

 radiating riblets ; inside white, margin spotted. This beautiful shell 

 is distinguished by scabrous striae, with noduliferous or chain-like 

 ribs at intervals. (Sowb.*) 



Falkland Is. 



F.polygona SOWB. Thes. Conch, iii, p. 186, f. 177, 137. 



F. EXQUISITA Reeve. PI. 32, fig. 34. 



Shell ovate, scarcely attenuated anteriorly, thin, rather depressed, 

 raised in the middle, radiately closely ridged, ridges somewhat ir- 

 regular, corrugated, obscurely nodulous, orifice very large, con- 

 tracted at the sides ; yellowish-white, conspicuously regularly rayed 

 with purple-black ; internal margin tessellated, (five.) 



Straits of Magellan. 



F. exquisita RVE. Conch. Icon. f. 74, 1850. 



F. STELLATA Reeve. PI. 32, fig. 32. 



Shell ovate, depressed, rather elevated in the middle, obscurely 

 rayed with ridges which are obsoletely nodulous ; orifice oblong, 



