201 



g- - 



— C. St. 



anterior portion, lying ensheathed in a thick-walled style-sac. This 



sac (Fig. 1 c. sc.) is situated within the lower portion of the stomach 



on the convex border, and is bounded on the other side by the 



narrow anterior chamber which 



eventually leads into the intestine 



{int.). Surrounding the aperture of 



communication between the stomach 



and style-sac, is a conspicuous fold, 



and in some of the specimens which 



were examined the head of the style 



projected a short distance beyond 



this fold into the posterior chamber 



of the stomach. The crystalline 



Fig. 1. Stomach of Turitella eommimis 

 (\( 6). c. g. crescentic or caecal groove, c. sc. 

 crystalline style-sac. c. st. crystalline style. 

 tnt. intestine, oes. oesophagus. 



style (c.st.) is a semi-translucent, rod-like body of a gelatinous con- 

 sistency ; it differs in no way from similar structures found in other 

 molluscs. 



This crystalline style-sac is, however, not the only feature of 

 interest that the stomach of Turritella presents. There is on the 

 inner wall of the posterior chamber a short crescentic groove (c. g.) 

 bounded by tumid lips, which lies in close proximity to the aperture 

 of the oesophagus. This structure is noticeable on the external sur- 

 face of the stomach as a slightly protuberant crescentic swelling of a 

 somewhat lighter colour than the surrounding part. On the opposite 

 side of the stomach and overhanging this groove, is a fleshy ridge, 

 the fleche tricuspide, which is covered with a gelatinous cuticular 

 secretion of the same character as the crystalline style. This struc- 

 ture is not represented in the figure, it is of very variable occurrence, 

 in some specimens often attaining a large size, in others, being in- 

 significant, or even wanting. 



It was after a comparison of the internal structure of the stomachs 

 of Trochus and Turritella that the significance of the crescentic 

 groove {eg) in the latter, became apparent. In the stomach of 

 Trochus (Fig. 2) a groove {eg) bounded by tumid lips is present, 

 running up to, and continued throughout the spiral caecum is. c). 

 As in Turritella, this groove commences near the aperture of 

 the oesophagus, and after proceeding a short distance receives the 



