NOTES ON GONIDEA ANGULATA LEA, A FRESH- 

 WATER BIVALVE, WITH DESCRIPTION 

 OE A NEW VARIETY 



By WM. H. DALL 

 Curator, Division of Mollusks, U. S. National Museum 



The National Museum contains the original type of Lea, the type 

 of Gould's A. feminalis, a cotype of A. randalli Trask, and specimens 

 agreeing well with the figure of Sowerby's A. biangulata, together 

 with a good series from some twenty different localities, ranging 

 from Spokane, Wash., south to Los Angeles, Cal. These specimens 

 show the species to occur in the watersheds of the Columbia River 

 and its branches, of the Umpqua River, of the Sacramento and San 

 Joaquin rivers, the Santa Clara Valley, and the valley of Los 

 Angeles. 



All the named forms are markedly angular ; the secondary radial 

 rib present in all of them is especially prominent in the form called 

 biangulata by Sowerby. 



The valves may be compressed or inflated, the angle may be blunt 

 or carinate, the posterior end, always wider than the anterior, may 

 be very or only moderately wide, dorsally alate or merely angular. 

 The anterior end is short and rounded or, in some specimens, very 

 attenuate and almost pointed. 



The periostracum is yellowish brown, darker in the older parts, 

 varying to black; when light it is frequently elegantly rayed with 

 dark green. The hinge teeth are conspicuous in the young, but 

 obsolete in the adult; the surface is more or less concentrically un- 

 dulate. The nacre is livid bluish white or with a salmon-colored 

 flush in the concavity of the valve, all salmon-colored, or elegant 

 purple partially or throughout. The maximum length was 5^4 

 inches ; a specimen in the collection 4.5 inches in length has a width 

 of 2)4, inches, but the majority are more slender. The young, 

 40 mm. long, may have a well-developed lateral carina or be entirely 

 destitute of angulation. 



Mr. Harold Hannibal, of Santa Clara County, California, has 

 recently sent to the Museum a fine series of specimens from Guad- 

 alupe Creek, between San Jose and San Francisco Bay, which are 

 remarkable for the almost total absence of lateral angulation, their 

 large size, compressed form, and freedom from erosion. Hardly 

 any trace of the angulation is left, and in this character all agree; 

 6 499 



