S6 SOUTHERN CALIFORNIA ACADEMY OF SCIENCES. 



more than others, of immature eyes; these are found on the man- 

 tle border on either side of the mature ocelli. The number of 

 fully grown ocelli in each specimen varies from about 46 to 50; 

 23 to 25 in each valve. These eyes are not situated at equal dis- 

 tances, nor do they lie one in each scallop. In a specimen num- 

 bering 21 ribs on one valve there were 23 large ocelli besides the 

 undeveloped ones. 



Branchiae or Gills: The branchiae or ctenidium are double and 

 there are two , one on either side of the body . They are semi-circu- 

 lar in shape ( Fig .1,2 and 8 , plate V ) . They extend on either side of 

 the body from under the liver — which is situated on the anterior 

 portion of the shell just below the dorsal margin — ^across to the 

 adductor muscle around to the point where the rectum lies close 

 to the adductor muscle. At this point both the double gills 

 meet, but are not attached to each other. The gills are attached 

 on the inner circle to a white, translucent, crescent shaped mem- 

 brane (Plate V, figs. I and 3). This membranous body is in 

 turn attached to the adductor muscle excepting at the extreme 

 posterior end where for % inch this transluscent body is free. 

 This is just above the end of the rectum. The gill membrane is 

 not so filmy as the mantle and is very much thicker. The 

 branchiae or gills are composed of transparent tubes or filaments 

 (Figs. 12,6 and 7 plate V). These are easily broken asunder, 

 when the gills appear only like single tubes attached at the top. 

 The connective tubes or tentacular junctions when present are 

 plainly discernable under the microscope. The edge of the gills 

 are formed of deep scallops — not seen by the naked eye- — under 

 the microscope each scallop is found to be composed of about 17 

 scallops. 



The color of the branchiae is a yellowish brown, but under the 

 dissecting glass each tube is of a bright yellow color before the 

 animal has been placed in alcohol. 



Foot: Tongue shaped and small. (Figs. 3, 5 and 7, plate IV, 

 has a groove on the under side (a. b, fig. 8, plate IV) next to 

 the byssal notch in the shell. In adult specimens there is no 

 byssus present. I once found an exception to this rule when the 

 animal had three or four strong byssal threads growing out of 

 the foot. 



Adductor muscle is large and is situated below the dorsal mar- 



