268 CHARLES HOWARD EDMONDSON 



of Mya arenaria, almost completely separated from the intestinal 

 tract. 



I have not observed spirochaetes in the styles of any forms in 

 which the style sacs are separated from the intestinal tracts, al- 

 though the parasites are at times abundant in the stomachs and 

 intestines of some of these clams, especially Schizothaerus nut- 

 tallii and Mya arenaria. I have commonly found .spirochaetes 

 in the crystalline styles of Saxidomus giganteus and Paphya 

 staminea, in both of which species the style sac is connected with 

 the intestinal tract throughout the length of the former. The 

 presence or absence of these free-moving parasites in the crys- 

 talline style also assists, I believe, in establishing the relative 

 consistency of this organ in different species of lamellibranchs. 



The mature crystalline style of Mya arenaria (fig. 4) is cylindri- 

 cal, becoming slightly thicker toward the extremity which pro- 

 jects into the stomach, which I shall designate as the proximal 

 end, tapering gradually toward the rounded distal extremity 

 which rests against the base of the foot of the clam. In its course 

 from the base of the foot of the clam to the stomach the style 

 approximates, in an imperfect manner, the arc of a circle (figs. 

 1 and 2). On the ventral surface of the visceral mass, for a dis- 

 tance of from 20 to 30 mm. in a medium-sized individual, the dis- 

 tal portion of the style sac is exposed to view in the midline. 

 From this exposed region, as the crystalline style disappears into 

 the visceral mass, it inclines to the left of the midline in its course 

 toward the stomach entering that organ through its posterior 

 ventral wall. 



The size of the crystalline style of Mya is dependent, in gen- 

 eral, upon the size of the animal possessing it. During digestion 

 the proximal or stomach end of the style is worn away more or 



Fig. 4 Mature crystalline style of Mya arenaria. X 2j. 



Fig. 5 Transverse section of the crystalline style showing the concentric lay- 

 ers and spindle-shaped masses of mucus. Mc, mucus masses. X 22. 



Fig. 6 Longitudinal section of a portion of the crystalline style, greatly en- 

 larged. Mc, spindle-shaped masses of mucus. 



Fig. 7 Horizontal section through the floor of the stomach showing the begin- 

 ning of the style sac and the intestine. St, stomach cavity; Ss, style sac; Gs, 

 gastric shield; Int, intestine. X 25. 



