ON THE VARIATION OF IHE SHELL OF 
PECTEN IRRADIANS LAMARCK 
FROM LONG ISLAND. 
C. B. DAVENPORT. 
Tuis study is concerned with the shells of the prevalent 
species of scallop, Pecten zrradians, from Cold Spring Har- 
bor, Cutchogue, Fire Island Beach, and Oak Island Beach, 
Long Island, state of New York, collected during August and 
September, 1899. 
Pecten (Fig. 1) is a genus of bivalve Mollusca whose nearly 
circular valves are provided with a number of ridges radiating 
from the beak at the hinge. The hinge is elongated tangen- 
tially, forming a pair of **ears" where the ends of the tangent 
depart most widely from the circle. The ears of the two 
valves are very different, as, indeed, are the conditions to 
which the two valves are subjected in nature. For when 
Pecten is about three millimeters in diameter it attaches itself, 
so that it lies in a horizontal fashion, by means of a byssus. 
It remains attached until it is from ten to thirty millimeters 
long, after which it lives free. The byssus passes to the 
exterior between the anterior ear of the right valve and the 
main body of the shell ; consequently, when the right valve is 
viewed exteriorly, the right-hand ear is deeply notched,? while 
the left-hand ear is not notched at all. In the left valve both 
! As it is necessary nowadays to recognize that a specific name by itself means 
very little, a string of synonymy must be appended. Recent names for the 
“species” or “variety” to which the form-units that I studied belong, are: 
Pecten (Plagioctenium) gibbus, var. irradians (Dall, '98, p. 748), and Chlamys 
(Egquipecten) irradians (Verrill, '99, p. 77). Dall recognizes two northern varie- 
ties of gibbus : “ gibbus var. borealis ” of the New England coast, and “ gibbus 
var. irradians" “from New Jersey” south. Neither of his descriptions of these 
two forms agrees closely with the Cold Spring Harbor form-unit, which might 
therefore receive a new varietal name were not the futility of this endless naming, 
alas, too evident. 2 Fig. 1, top. 
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