178 CERION. 



In C. incanum, dissected by Leidy, C. mumiola by Poey, and 01 

 yumaense, by Vanatta, the penis retractor is short. In C. yumaense 

 no spermathecal diverticulum was found, but I think this was due to 

 the very poor preservation of the specimen dissected. 



Young shells of this genus often have the aperture contracted by 

 teeth, formed a short distance within the lip-edge, and subsequently 

 absorbed in most cases. Two of these teeth are upon the parietal 

 wall, two within the basal lip, and one upon the columella, the latter 

 being the end of the continuous columellar plait, and present in the 

 young of all species. In species having such teeth, when young, 

 they are not present at all stages of growth, but only appear at 

 intervals. 



In C. uva only one of the basal teeth is usually visible from the 

 mouth, the other being added with subsequent growth, deep in the 

 throat. They often persist in adult individuals in this species only. 



In G. copium (group of C. pannosum, Cayman Is.) there are two 

 basal teeth, the outer smaller, and one tooth above, or none (pi. 47, 

 fig. 31). 



In C. yumaense a large series of young shows none with teeth ; nor 

 are any present in specimens of C. y. salki G. crassilalris examined, 

 all belonging to the group of C. crassilabris. 



G. incanum sometimes has teeth, two above and two below, but 

 most of the young shells examined have none. One young multicosta 

 examined has no teeth. 



G. mumia has one basal and two upper teeth, or is without any. 



One young G. regina has a single rudimentary inner basal tooth, 

 others being toothless. 



One specimen of G. glans (form agava) has a rudimentary basal 

 tooth, others being toothless. In G. milleri (pi. 36, fig. 47), four 

 teeth are found. In a form of glans from Andros, Mr. Maynard 

 found four teeth. 



No sufficient data exist for testing the value of the teeth of the 

 young as an indication of affinities. Collectors should secure large 

 series of young shells, as the subject is one of some interest. Whether 

 these teeth are lingering vestiges of a former adult dentition, or are 

 an adaptation pertaining to the young stages only, remains problem- 

 atic. Certain forms of Holospira have a somewhat similar internal 

 structure. 



