1889.] NATURAL SCIENCES <>K PHILADELPHIA. 275 



tip near the siphonal opening. Its margins are smooth and .simple. 

 < Opposite the pedal opening a part of the foot is produced and thick- 

 ened, anteriorly sharp edged, rounded behind, and having a spongy 

 sole with a small deep (glandular?) sinus near its anterior end ; this 

 portion some observers would probably regard as constituting the 

 whole foot, but to me the view that it represents something analogous 

 to the pedal disk of Pecten, seems more natural. In the sinus above 

 the posterior end of the foot (as above defined) and in the median 

 line, is a slender subcylindrical process (about 5*0 mm. long as con- 

 tracted in spirits) probably a sensory organ like that of Yoldia. 

 Directly behind this is the atrium of the incurrent siphon, a small 

 chamber hermetically roofed by the branchia which are united by 

 a thin membrane so as to entirely cut off the branchial from the 

 anal chamber. This membrane is continuous with, or firmly 

 attached to, the siphonal septum. Directly behind the chamber 

 the passage-way or tube of the siphon contracts, though there seem- 

 to be no curtain valve. The branchia terminate at the anterior end 

 of the siphonal septum. The gills fall in two double lamellae on 

 each side. The inner gill is a simple elongated flattened sac, the 

 outer one has its inner wall dependent, then, at the distal edge, 

 folded back upon itself and continued upward, dorsally, beyond the 

 point of starting, so that the free edge forms a narrow "appendix." 

 The viscera present no special points of interest. There is a large 

 " hyaline stylet " which is contained in a larger chamber extending 

 nearly to the front end of the foot. The other end of the stylet is 

 attenuated, sharply bent, and projects into the cavity of the 

 stomach. The visceral mass is large, the intestine much convoluted, 

 the anus projecting, large, involute and cupshaped, constricted be- 

 hind the " cup." The anterior adductor is normal but feeble ; the 

 muscle passes from the reflected shell margin in one side straight 

 across to the other. The posterior adductor is oval in section and 

 considerably stronger. In the right valve is a slender, prominent, 

 compressed fossette carrying a small thin, internal cartilage, which 

 is attached to the opposite valve upon a small sharp not-excavated 

 shelly process. This remnant of the original cartilage may assist in 

 keeping the valves attached to one another, though it is very feeble, 

 but it has wholly lost its original function of an elastic cushion to 

 prevent the too sudden or rude closing of the valves. It is doubt- 

 ful if the thin shred of horny epidermis behind the beaks in this 



