214 BULLETIN OF THE 
adult; in very young specimens they are absent, and the shell can hardly be 
distinguished from P. imbrifer, which has commonly been confounded with it, 
as mentioned under that species. The present one is characterized by the very 
large shelly bubbles, generally worn away, and leaving their semicircular basal 
edges plainly visible in fifteen to eighteen series, with intercalary ones near 
the margin. The umbo of the upper valve has sharp elevated concentric 
ridges without pustulations. There are inside near the margin of adult shells - 
17-21 short lire, thickest at their distal ends usually and not extending into 
the hollow of the shell, except the marginal ones, and these not always. The 
shell is very thin, vitreous, and pale yellowish in color. 
Amusium (Propeamusium) Holmesii Dati. 
Plate V. Figs. 5, 11. 
Shell small, somewhat oblique, thin, brightly colored (like A. var. marmo- 
ratum), the convex valve with twenty to twenty-eight faint radiating ridges, 
absent toward the beaks and with intercalary ridges toward the margin ; inter- 
spaces between the ribs polished, mostly smooth or with traces of concentric 
lamelle which near and over the radiating ridges rise to arched scales, which 
in some cases are closed in front, forming spindle-shaped pustules, with the 
longer axis in the concentric line to which they belong; anterior ear the larger, 
pectinately scaled on the margin, with obscure radiating or lamellar sculpture ; 
concave valve finely concentrically waved, the waves becoming crowded and 
scaly toward the margin ; anterior ear with three or four radiations and strong 
lamelle, posterior ear lamellate, but not radiated ; anterior margin rounded, 
posterior ditto, produced. Alt. 12.0, lon. of shell 12.0, of hinge line 6.0, 
max, diam. 2.0mm, Internal lire eleven to fourteen, fine, with a tendency 
to pair, and falling considerably short of the margin in the completely adult 
shell. 
Dredged at Station 273 in 103 fms., and in 100 fms. at Barbados, living. 
The bottom was yellow coral and broken shell, and the temperature 59°.5 F. 
This pretty shell is nearest A. Hoskynsi Forbes, from which it differs by the 
polished umbonal region, the larger number of ribs, the smaller size and differ- 
ent shape of the pustular scales, by its larger size, differently proportioned 
and pectinated ears, and by the strength, number, and character of its internal 
lire. Its form is nearest that of A. Pourtalesianum, var. marmoratum, which 
is also brightly colored. It is named in honor of Dr. Holmes, the author of 
the “Pliocene Fossils of South Carolina.” 
Amusium (Propeamusium) Sayanum Dat. 
Plate V. Figs. 3, 9. 
Shell compressed, nearly equivalve, somewhat inequilateral ; white ; with 
dissimilarly sculptured valves; right valve with (near the middle) about 
