A. E. Yerrill — Study of the fmnily Pectinidm. 73 



The bases of the outer ones are broadly connected with the mantle 

 lining, and thus enclose the anterior ends of the gills. 



Around the mouth are about ten much-branched, unequal, brown, 

 labial tentacles, which are extensively webbed together. Of these, 

 three are at the posterior side of the mouth, one large median one, 

 much divided, and one much smaller one on each side ; a large 

 much-divided lateral one lies on each side, at the base of the inner 

 palpus ; a still larger and more branched one lies at the base of each 

 outer palpus ; three small ones united to the others by a web, lie in 

 front of the mouth. The foot (pi. xx, fig. 9) in alcohol is oblique, 

 stout at base, suddenly contracted at the distal third and again 

 slightly enlarged at the blunt tip. Its anterior face is turned to the 

 right and has a large byssal groove extending to the distal constric- 

 tion ; at the tip there is a very small deep slit, of which the sides 

 can be somewhat expanded ; this slit is entirely separate from the 

 byssal groove. In the breeding season the abdomen is prominent 

 and crowded with eggs ; it projects downward, and bends abruptly 

 backward, terminating in a small, sharp papilla. Gills foai", of the 

 normal fillibranchiate structure. Pallial tentacles very numerous 

 and unequal, the outer ones smaller and much crowded. Ocelli con- 

 spicuous ; there are generally three between every two of the 

 primary tentacles. 



Young specimens (pi. xvi) when 4°""^ long and 4 5™™ high, show an 

 irregular " camptonectes sculpture," together with small and simjjle 

 radial ribs. The byssal notch is broad and angular, but rounded at 

 bottom ; three pectinidial teeth are developed. 



Those that are 8™™ long and 9-5™'" high have four acute pecti- 

 nidial teeth, and a broad notch, i-ounded within. The ribs have 

 become stronger and the edges of the shell are scalloped. The 

 valves gap slightly at the anterior end and at the ends of the auri- 

 cles. Near the margin, especially of the left valve, concentric 

 sculpture appears, and by crossing the ribs produces a scaly appear- 

 ance. 



Var. insculpta, nov. 



A variety is occasionally taken on our northern coasts, which has 

 a more elaborate sculpture than usual. The concentric and diver- 

 gent laminae and smaller radial riblets cross each other in such a way 

 that a peculiar decussated sculpture is formed between the primary 

 ribs on the early part of the shell, while on the older parts the inter- 

 spaces are covered with elevated scales. The surface rises into six 



