2366 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
gon, and which also extends to the Gulf of Panama, but that species, instead of 
having six or seven anterior radial channels like 8. agassizii, has from nine to 
twelve; the projections of the periostracum are much longer on the anterior part 
of the shell than posteriorly, giving a subtriangular profile (as figured in Proc. 
U.S. Nat. Mus., 17, plate 25, fig. 1894). 
It is difficult to be dogmatically confident as to specific limits in forms like 
these when one has only more or less imperfect; valves without the soft parts, and 
especially modifiable by the results of drying. If in future these three species 
ever become known through abundant material and prove to be merely variations 
of a single type, it will show a marvellous distribution from Puget Sound, south 
to the Straits of Magellan. But I have not seen any unmistakable specimens of 
S. macrodactyla from north of the Island of Chiloé, on the Pacific side. 
Solemya (Petrasma) panamensis DaArr, n. sp. 
Shell thin, elongate-oval, the posterior end more pointedly, and the anterior end 
more bluntly, rounded ; periostracum brown, brilliantly polished, recurved over 
the margins of the valves, not produced into long processes, though more or less 
broken up outside of the margins; anterior part of the shell radiately marked 
with eight or nine obscure rays, which are more crowded in front and dorsally; 
the middle of the valve with a few sparse rays, the posterior part having six OT 
seven more closely adjacent, followed by a smooth unradiated area behind the beaks 
and above a line drawn from them to the middle of the posterior end of the valve; 
beaks flat, with a lozenge-shaped area of ligament; visible behind them ; inferior 
bluish, translucent ; the chondrophore strong, projecting obliquely into the cavity: 
its front margin prolonged as a narrow, elevated rib very obliquely backward in 
front of the posterior adductor scar; muscular impressions rather obscure; in- 
terior of the valves faintly radiately striated. Lon. of valve exclusive of the 
periostracum, 39.0 ; alt. 15.0; diameter, 8.0 +; the beaks in front of the posterior 
end, 14.0 mm. 
U. 8. S. “Albatross,” station 2799, Panama Bay, in 294 fathoms, mud. 
U. 8. N. Mus, 110,678. Also at 2973, off Santa Barbara, California, in 68 
fathoms, mud, bottom temperature 54° F. 
This is more expanded in front and less sharply truncate in front than S. agas 
sizii of the same length, and they may be separated at once by the difference in 
the hinges. $. valvulus Carpenter is a much smaller species and has no anterior 
prop to the chondrophore. 
An examination of specimens of Pthonia, Clinopistha, Dystactella, and Solemya, 
from the Palaeozoic beds of the west, shows that all the groups except the last 
have the valves completely closed, the periostracum not extended beyond the 
valve margins, and the ligament external, Solemya radiata Meck and Worthen, 
a fine species from the Carboniferous of Illinois, has the ligament external and 
the hinge apparently very similar to that of jS. agassizii. The other characters; 
however, would hardly allow it to be united in the same subgenus. 
