152 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
depression does not show in the adult shell. 
bears to the soft parts within I do not know. 
What relation this 
PECTEN TENUICOSTATUS Mighels and Adams. 
Fig. 9. Length, 32 mm. 
Professor Drew has described and figured this species in so 
complete a manner that it is not necessary to comment on it 
further in these general notes. Dr. R. T. Jackson has also dealt 
with the protoconch and other early stages of the shell in his 
memoir (Mem. Boston Soc. Nat. Hist., 1890, vol. 4, no. 8). I can- 
not forbear, however, to figure an early stage of this species show- 
FiG. 9. — Pecten tenuicostatus Mighels and Adams. 
ing its remarkable resemblance to certain avicular forms (c) . In a 
specimen thirty-two millimeters in diameter the marginal ten- 
tacles from one to five millimeters long are crowded around the 
entire mantle margin including the sides to the very tips of the 
hinge margin. In the broad expanse of the mantle border two 
papillae are seen out of place. None of the papillae were found 
bifurcated. 
