542 



PROCEEDINGS OF THE ACADEMY OF 



[Dec, 



Fig. 5. — Acmoea sp. 



Section of protoconch with portion of young still within it. 

 Shell stippled. 



more striking appearance of a coil is obtained. This is true of both 

 sides of the protoconch. The lateral edges, then, of this ridge 

 shown in the median sections of the shell are simply turned back 

 or " coiled " to a greater degree than the central part and the lateral 

 marks are the external evidences of this condition, the "folds" 

 being the union of the ridge with the outer wall of the shell. This 

 is shown in figs. 2 and 6. 



If this were a true coil the lines of growth would be expected to 

 bear it out. By observation under the high powers in direct re- 

 flected light it is possible to discern these lines in the species under 

 consideration. They are very regular, clear, and well marked. In 

 fig. 3 a camera lucida drawing is shown. Their center seems to be 

 on the lower surface of the protoconch. Those of the lateral pouches 

 are shown to be parallel to their long axis and not conformant 

 below the shell to those behind them. What the significance of this 

 state of affairs may be I cannot hazard a guess, and it appears as 

 though its explanation must await the complete working out of the 

 embryology which Patten was unable to carry so far. The embryo 

 in the youngest stages which I sectioned occupies these corners 

 with portions of the liver. Judging from the lines of growth, one 

 would be tempted to think that these pouches were formed later 



