1909.] NATURAL SCIENCES OF PHILADELPHIA 535 



in the length. The surface is smoothish except for growth-lines which 

 are strongest near the lower margin and anterior end. Color various 

 shades of brown, with rather indistinct darker or greenish rays, chiefly 

 on the posterior half. The beaks are low, at the anterior fifth of the 

 length. When perfect they have double-looped concentric sculpture. 

 Valves thin, lined with nacre which is whitish in the cavity and anter- 

 iorly, but pink and very iridescent posteriorly (sometimes suffused 

 with pink throughout, darker and purplish below the pallial line, or 

 sometimes silvery white throughout) . Pseudocardinal teeth compressed, 

 rather small; lateral teeth very short, about one-third the shell's 

 length. Ligament short. 



Length 47, alt. 26i, diam. 16^ mm. 



47, " 26, " 15 " 

 Ganina River three miles southwest of San Dieguito, in mud and 

 gravel in clear water about knee-deep, where there was no current. 

 Also in the Valles River two miles above Mecos. 



Some specimens of the type lot are larger, length 55, alt. 28, diam. 

 16 mm. There is also some variation in the teeth, which may be more 

 or less stout. 



In the Valles River at Mecos the shells are rather small and not 

 incrusted; nacre white, iridescent posteriorly, but not suffused there 

 with pink or purple. Some of the half-grown specimens are quite 

 fully rayed. 



Two miles above Mecos in the Valles River there are large shells 

 with but little incrustation, and rather dull, opaque, white nacre, 

 with but little iridescence. Two measure: 

 Length 58, alt. 34, diam. 19 mm. 



" 56, " 28i, " 19^ " 

 L. semirasa differs from L. signata and L. undivaga by lacking 

 corrugation on the convexity of the valves and on the posterior-dorsal 

 slope. It apparently lives with the shell nearly half buried, somewhat 

 more than the posterior half projecting, and in most localities covered 

 with a hard calcareous coat, as in pi. XXVI, fig. 9. Fig. 7 represents 

 a cleaned specimen. 



Lampsilis popei (Lea). 



Unio popei Lea, Obs., VIII, p. 51 (Devils River, Texas, and Rio Salado, 

 Nuevo Leon, Mexico). 



Valles River at Valles, Willis' ranch, and two miles above Mecos. 



Abundant. Tampamolon Creek, one specimen. The shells have fine 



purple nacre, coppery and iridescent posteriorly. I have compared 



them with the types of popei in U. S. National Museum. 



