grooves which are densely ciHated. In this form, (figs. lo and 

 12, Ip.) the portions of the palps that lie along the sides of the 

 body are of this character but the portions above and below the 

 mouth are ruffled so they form a large conspicuous mass that 

 entirely conceals the mouth. What purpose is served by this 

 ruffled portion that would not be served as well by the simpler 

 arrangement has not been determined. 



Both palps are free only along their ventral borders. The 

 outer palps, which correspond to the upper lips, are united to 

 the body wall above the mouth and along their dorsal borders. 

 The inner palps, which correspond to the lower lip, are united 

 to the body wall below the mouth along their dorsal borders and 

 have their inner surfaces continuous with the inner surfaces of 

 the outer palps. Their posterior borders, which are not as 

 extensive as the corresponding posterior borders of the outer 

 palps are united to the body wall. 



Food from the gills passed between the palps is conducted by 

 the cilia covering their opposing surfaces to the corners of the 

 mouth, of which the grooves formed by the union of the dorsal 

 borders of the outer and inner palps are continuations. 



GILLS. 



As in most lamellibranchs the gills (figs, ii, 12 and 19), are 

 four in number, there being two on each side of the body. Each 

 of these gills appears as a thin and delicate striated membrane 

 that runs from near the mouth, around the ventral side of the 

 adductor muscle to and a little beyond the anal opening. The 

 gills are very similar in appearance, pointed anteriorly and pos- 

 teriorly and marked by distinct striations that radiate from their 

 lines of attachment near the adductor muscle, toward their free 

 borders. With proper illumination very fine striations may be 

 seen crossing these at right angles. 



Each gill consists of two thin membranes, called lamellae 

 (figs. 17, 18 and 19), that lie very close together and are 

 attached to each other at intervals corresponding to the radial 

 striations of the gill. Each pair of gills is suspended by a mus- 

 cular membrane (figs. 19 and 20, sm.), most of the muscles of 

 which are inserted on the corresponding shell valve near the 



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