NOTES ON SPECIES 489 



Lima f sp. a. — Shell inflated, most so in umbonal region, the posterior 

 umbonal slope being the more abrupt, and convex in outline ; the anterior 

 margin is slightly concave in outline. Ears small, slightly -aneqiial, the 

 anterior one being separated by a rounded groove; the posterior ear, 

 apparently very faint, merges gradually into the body of the shell. Beaks 

 pointed, incurved. Hinge area very broadly triangular, with apparently 

 a central resiliifer. Teeth and muscle impression unobserved. Surface 

 smooth. Length of a large specimen from beak to front, 22 millimeters; 

 Greatest width anterior to mid-length, 18 millimeters. 



Lima f sp. &. — This form differs from Lima f sp. a in its smaller size 

 (length of average shell, 15 millimeters; greatest width, 12 millimeters), 

 its radially striate surface (twelve rounded striae in the space of 4 milli- 

 meters; these are separated by equal interspaces; the concentric growth 

 lines thus give to the shell a minutely cancellate appearance), and in 

 having its beaks turned toward the convex margin (instead of toward the 

 concave one, as in species a). It was at first thought that species a and h 

 might be opposite valves of the same form, but we apparently have in 

 our collections both valves of species h (though only the right one of 

 species a). 



Lima sp. c. — Shell inflated, though less so than in the preceding species. 

 Beaks pointed, separated by a lozenge-shaped area, over which radiate 

 grooves from each beak. Interior unknown. In external appearance it 

 somewhat resembles Aviculopecten guadalupensis Girty,^ from the Guada- 

 lupian Permian of Texas. In each the anterior ear is separated from 

 the body of the shell by a prominent, curved, angular groove. But the 

 alternation of broad and rounded with narrow, angular ribs is lacking in 

 Girtv's species, as apparently is also the rather distinct posterior ear. In 

 each the radiating ribs number about 20 to a valve, and in length, from 

 beak to opposite edge of shell, Girty's specimen measures 15 millimeters, 

 while ours average 20 millimeters. 



Asiartella gurleyi White. — Three minute specimens, about 4 milli- 

 meters long and high, .are identified with White's species. Except that 

 our specimens are smaller (White's type measuring 7 millimeters in 

 length and height) and with a weaker umbonal ridge than is figured/'^ 

 they agree well in the subsquare shell outline, low umbos, and in the sur- 

 face sculpture, broad concentric furrows separated by sharp linear ridges. 



Patellostium nodocostatum (Gurley). — Our numerous specimens ap- 

 proach this species rather closely; an average mature shell measures (in 



9 U. S. GeoL Survey, Prof. Paper 58, 1908, p. 436, pi. 16, fig. 20. 



10 C. A. White : Contrib. to Inv. Paleont., nos. 2-8, 1880, pi. 42, figs. Qa-h. 



