1912. 



.NATURAL SCIENCES OF PHILADELPHIA. 



543 



than the middle portion of the protoconch and subsequent to a 

 resorption of the posterior edge. If they were remnants of a true 

 coil it would be expected that growth should take place in them 

 first. 



As mentioned above, the liver, at the earliest stage I had, occupied 

 a part of the protoconch with its large granulated cells (fig. 5). 

 In company with it was one loop of the large, thin-walled alimentary 

 canal. This is well past the veliger stage and when the embryo 

 is fairly complex. There were no gills present. At a period slightly 

 later than the stage represented in fig. 1, the protoconch is broken 

 off, leaving a cicatrix. The lower part of the primitive shell seems 

 in some cases at least to remain on the patelloid shell to form the 

 posterior part of the cicatrix. This has been fully described by 

 previous authors. 



In conclusion, it may be stated that the protoconch gives more 

 evidences of being a simple caecal-like shell than coiled, although 

 the evidences are open to other interpretations. The slight coil of 

 the body and shell and a tendency of the shells to form more rapidly 

 anteriorly than posteriorly at first would indicate the presence 



Fig. 6. — Protoconch and beginning of permanent shell of Acmcea sp. in optical 

 section, from dorsal surface, r, Ridge at upper line of lateral pouch. 



