510 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.xxiv. 
of grooves on the internal margins of the valves. These grooves are 
subconcentric but cut the margins more or less obliquely, not in har- 
mony with the lines of growth. The same type occurs in our southern 
tertiaries, and an attempt is made in fig. 7 to illustrate this system of 
marginal grooving. 
MERETRIX SIMPSONI Dall. 
Plate XXXll, fig. 3. 
Cytherea simpsoni Dall, Bull. 37, U. S. Nat. Mus., 1889, p. 56 (name only); 
Nautilus, IX, 1895, No. 1, p. 10. 
Tampa, Florida, Charles T. Simpson; Sarasota Bay, Hemphill. 
U.S.N.M., 53792. 
Shell with narrow, slightly irregular and feeble concentric ridges, 
surface not polished except over the large ovate lunule which is 
smooth. Colors white or more or less suffused with purple which 
may be very dark internally, a zigzag pattern of yellowish brown fre- 
quently present; pallial sinus ascending, rather large and rounded in 
front; margins entire; escutcheon not delimited. Lon. 16.5; alt. 15.0; 
diam. 8.5 mm. The shell is rather solid and the periostracum thin 
and translucent. 
MACTRA RICHMONDI Dall. 
Plate XXXI, fig. fi. 
Mactra richmondi Dall, Nautilus, VIII, 1894, No. 3, pp. 26, 28. 
Grey Town, Nicaragua, C. W. Richmond. U.S.N.M., 124774. 
The single valve obtained is white but may be somewhat bleached. 
MACTRELLA IHERINGI Dall. 
Plate XXXII, fig. 8. 
Mactrella iheringi Dall, Nautilus, X, 1897, No. 11, p. 123. 
San Paulo, Brazil, Ihering. U.S.N.M., 107632. 
The shell is white with a yellowish silky periostracum and may 
reach nearly 3 inches in length. 
ASTHENOTHiERUS HEMPHILLI Dall. 
Plate XXXI, fig. 9. 
Asthenothserus hemphilli Dall, Rep. Blake Pelec, Bull. Mus. Comp. Zool., XII, 
1886, No. 6, p. 308. 
West of Florida in 17 fathoms; Marco, Florida, in 2 fathoms, Hemp- 
hill. U.S. N.M., 53691. 
Small, yellowish white, with the aspect of a very young Periploma. 
