OF CONCHOLOGY. 153 



LEDIDiE. 

 YOLDIA, Mcerch. 

 YOLDIA SEMINUDA, n. S. 



Shell obscurely lozenge-shaped, elongate, covered with a pol- 

 ished, glossy, olivaceous epidermis. 



Valves compressed, umbones inconspicuous ; lunule long, nar- 

 row, just evident ; escutcheon long, narrow, indented, well de- 

 fined. Ventral margin arcuated, widest about the middle of the 

 shell; a slight obsolete groove or channel anteriorly, bordered 

 by two obscure ridges, terminates in a slight waved indentation 

 in the anterior ventral margin, about the middle of the anterior 

 fourth. 



Posterior end rising obliquely, rounded truncate posteriorly, 

 forming an angle of 90° with the hinge margin, and slightly 

 upturned. 



Posterior dorsal slope slightly concave, anterior slightly con- 

 vex, evenly rounded to the anterior end. Ligament pit large, 

 roundly triangular. Teeth (anterior) 37, (posterior) 17. Pal- 

 lial sinus reaching before the umbones, which are 14 35ths of the 

 whole length from the posterior end. 



Interior bluish white, with fine radiating lines. Exterior 

 marked by lines of growth and obsolete radiating lines ; sculp- 

 tured by sharp grooves, which, beginning near the middle of the 

 shell with a slight wave toward the umbones, pass backward and 

 downward across the lines of growth, rising a little and ceasing 

 abruptly at a distance of about 4-35ths of the whole length from 

 the posterior end. Lon. 1-74, alt. "82, diam. "27 in. 



Habitat, St. Paul's Harbor, Radiak, 17 fms. 



This shell is allied to Y. lanceolata, J. Sby., in which the 

 sculpture passes clear forward to the anterior margin. The lat- 

 ter is also a smaller, more globose and anteriorly rounder shell. 

 It is found in the same locality with the present species. Y. 

 Cooperi, Gabb, is another allied species, of widely different shape. 

 Y. seminuda is shaped much like Y. amydalea, Val., as figured 

 in the Thes. Conch., but is wider behind and more upturned, and 

 the anterior indentation is not conspicuous. That species is 

 without sculpture, and occurs in the same localities. 



Acila Lyalli, Baird, P. Z. S. 1863, has been referred to A. 

 eastrensis, but the sculpture and shape are quite distinct. I have 

 been indebted to the kindness of Mr. Jeffreys for typical speci- 

 mens from Vancouver, and have dredged it in 8 fathoms mud at 

 Sitka. 



Yoldia truncata, siliqua and intermedia, vars., were obtained 



