ACERHALA. A57 
The same type as P. ¢slandicus; but is small, more convex, the 
sculpture rather coarser. The groove between the auricle and body 
of the shell, which forms the byssal fissure, is remarkable for depth, so 
that the notch seems to be an emargination produced by the depth of 
the groove. It is also allied to P. rubidus, Hinds. 
Figure 571, exterior and interior lateral views of the shell; 571 a, 
lateral view of the shell; 571 4, details of sculpture. 
PECTEN HERICIUS (Gould). 
T. rotundato-triangularis, equilateralis, equivalvis ; valvis convexis, sub- 
tumidis : valva superior rosea, lineis extlibus concentricis exasperata, 
et costis ad viginti-quatuor, angulatis, alternis majoribus et spinis 
erectis fornicatis insculpta: valva inferior pallidior colore saturatiort 
zonata, costis subequalibus spiniferis armata; natibus acutis, promt- 
nentibus ; auribus obliquis valde inequalhibus radiatim squamoso-stria- 
tis: intus porcellana ; marginibus crenulatis, rosacets. 
Pecten hericius, Goutp; Proceed. Boston Soc. Nat. Hist., 11. 345. 
Dec. 1850. Expedition Shells, 95. 
SHELL triangular ovate, longer than broad, equilateral or a little 
oblique and equivalve: valves rather full, especially near beaks, whose 
sides rise abruptly from the ears: colour rose-red, paler and zoned 
with deeper red beneath; everywhere covered with fine radiating lines, 
which are rendered rough by erect and arched spines. There are 
about twenty-four radiating ribs. On the upper side these are alter- 
nately large and small, the larger ones crowned along the ridge by a 
line of long, erect, hollow spines; on the lower valve the ribs are 
nearly equal, the strie are coarser, and all the ribs are armed with a 
row of spines, though not so long as those on the upper valve. Ears 
oblique, very unequal, rayed with coarse, squamous strie. Interior 
porcelain-white, roseate at the edge, where it is finely crenulate. 
Length four and a half inches; height an inch and a quarter; 
breadth four and three-fourths inches. 
Inhabits the Straits of De Fuca, Oregon. 
115 
