THE NAUTILUS. 81 



retractive, pinched together and more prominent, and slightly angu- 

 larly bent, at the suture ; these are crossed by low rounded threads, 

 with wider interspaces, about a dozen on the penultimate whorl 

 between the sutures ; the surface is also finely sharply axially striate ; 

 the aperture is rounded, the outer lip slightly reflected and crenulate 

 by the spiral threads, but not thickened ; whorls more than five, 

 closely adjacent ; base (?); max. diam. 34 ; diam. at the truncate 

 apex 10.0 ; alt. of five whorls (the apex lost) about 60.0 mm. 



The type specimen of this fine species, consisting of internal and 

 external casts, was collected about five miles south of the head 

 of Port Moller, in the pass leading across Alaska Peninsula called 

 Low Pass Canon, U. S. Nat. Mus. 111072. Illustrations are in 

 preparation. 



(Published by permission of the Director of the U. S. Geological 

 Survey.) 



DESCBIFTION OF A UEXICAN LAMP8ILIS. 



BT H. A. PILSBRT AND L. S. FRIERSON. 



Lampsilis iridella P. & F. 



The shell is oblong, wider posteriorly, with the beaks at the ante- 

 rior two-ninths of the length ; anterior end rounded ; posterior part 

 sloping above, subtruncate at the end, compressed below the hinge. 

 Surface glossy, smoothish, obliquely corrugated along the posterior 

 slope (but sometimes very indistinctly so), and usually having a group 

 of short impressed lines or furrows vertical to the basal margin, near 

 the middle of the disk. Of a dull straw or pale greenish color, pro- 

 fusely marked with green rays, which are usually quite distinct and 

 narrow. The valves are thin, nacre bluish silvery, very iridescent 

 posteriorly. Cardinal teeth small, a single rather stout one in the 

 right valve, two more compressed and generally subequal teeth in 

 the left valve. Lateral teeth very narrow, double in the left, single 

 in the right valve. 



Length 49, alt. 26, diam. 15 mm. 



Valles, Mexico. Type no. 93810 A. N. 8. P., collected by 

 Mr. A. A. Hinkley. Cotypes in collections of Hinkley and Frierson. 



