] 34 THE NAUTILUS. 



epidermis, an obsolete umbonial ridge and deep, compressed beak- 

 cavities. It differs iu much the same manner from U. Lesleyi, which 

 has greater shell cavity. Compared with U. abacw Hald., it is pro- 

 portionally much wider, deeper and with more compressed beak- 

 cavities, and has not the checker-board markings of that species. 

 Old specimens resemble U. Pilxlryi Marsh, interiorly, but without 

 alation or undulations. In old specimens the base becomes emargin- 

 ate, and there is more or less biaugulation behind, and the teeth be- 

 come almost obsolete, and of a dull smoky tinge. Thirty specimens 

 were received. 



TTnio Friersoni sp. nov. PL III, figs, right and left. 



Shell smooth, triangular, inflated, nearly equilateral, obtusely 

 pointed behind ; sides swollen not constricted, rayless or obscurely 

 radiate when very young; substance of the shell uniformly rather 

 thick and solid. Beaks angular to the tips and with three or four 

 close undulations which form parallel V-shaped ridges with the 

 angle pointing down the umbonial angle, and the long straight arms 

 of which extend diagonally across the beaks. Ligament very short, 

 thin and of a lighter red than the epidermis, which is a dark-chest- 

 nut color, with minute strue and with coarse growth-lines. Um- 

 bonial slope obtusely angular. Posterior slope rounded on the 

 margin and with a raised ridge line from beak to posterior end, 

 forming there, generally, a slight biangulation. Dorsal area wide, 

 cordate. Cardinal teeth large, erect, with furrowed sides, the ante- 

 rior branch in the left valve being very thin and broad and with a 

 long striate edge. Lateral teeth short, slightly curved, the outer 

 one being the thinner. Anterior cicatrices distinct with a secondary 

 cicatrix above, aud running under the cardinal tooth. Posterior 

 cicatrices distinct. Dorsal cicatrices few and under the posterior 

 cardinal. Cavity of the shell very deep, and quite uniformly hol- 

 lowed out. Cavity of the beaks broad, roomy, the apex within 

 being nearly a right angle. Nacre usually white, with a tint of 

 blue, and iridescent at posterior end ; sometimes the nacre is entirely 

 pink. 



Animal always white. Size, width 2 inches, length 1'75, diameter 

 1-38. 



Habitat Bayou Pierre, an arm of the Red River in De Soto 

 Parish, Louisiana. 



My Cabinet, U. S. National Museum, Academy of Natural 

 Sciences, Pliila. and cabinet of L. S. Frier.-on. 



