8 EXPEEIMENTS IN THE BREEDING OF CERIONS. 



Cerion uva is stated by some writers to be without this median projec- 

 tion, but the specimens examined did not agree with this dictum. 



The radula presents some interesting variations in the 5 species 

 under consideration. The number of longitudinal tooth rows appears 

 to be practically constant. Cerion uva has 20-1-20, Cerion viaregis 

 22-1-22, Cerion crassilabris 23-1-23, Cerion casablancce 25-1-25, 

 Cerion incanum 27-1-27. These figures represent the rows which can 

 be readily counted. The marginal teeth become mere plates at the 

 extreme lateral margin, especially so in Cerion viaregis and Cerion 

 crassilabris. These plates terminate as irregularly shaped masses 

 which do not appear to be arranged in definite rows. It is therefore 

 somewhat difficult to determine the exact number that can be actually 

 counted in a given species, and this may account for slight differences 

 reported for the same species by different observers. The markings 

 on the marginal teeth can often not be made out with clearness; they 

 appear to be quadrangular, basal in most cases. There is a gradual 

 transition from laterals into the marginal beginning with about the 

 tenth tooth. The laterals are normally bifid with the inner cusp large 

 and rounded and the outer one much smaller and also rounded, but in 

 Cerion casablancce the smaller one is absent, though a few of the transi- 

 tional teeth, both laterals and marginals, show two cusps. The lateral 

 teeth are uniformly about twice as long as wide and are placed sUghtly 

 obliquely away from the rachidian tooth. The rachidian tooth presents 

 considerable difference in the different species. In Cerion crassilabris 

 there are three cusps, the central one appearing to be placed on a 

 lower level than the outside cusps. This same condition seems to 

 obtain in the laterals, the outer cusps being above the inner. In Cerion 

 viaregis there is but a single large rounded central cusp. In Cerion 

 casablancce and Cerion incanum two minute projections are found 

 bordering the median cusp. In Cerion uva the rachidian tooth is 

 broader than long, while in all the other species it is about twice as 

 long as broad. In this, too, the development of the lateral cusps is 

 enormous. 



The buccal mass differs little from the usual structure in Pulmonates. 

 The esophagus enters the top of the posterior portion. The two salivary 

 ducts discharge on each side of the esophagus at the junction of the 

 latter with the buccal cavity. The esophagus and the salivary ducts 

 pass beneath the cerebral commissure and over the buccal commissure. 

 The buccal gangUa are firmly attached to the buccal mass, one on each 

 side of the esophagus. The radula sack with the radula organ is 

 situated just below the esophagus and projects backward from the 

 distal end of the buccal mass. It extends from the radula sack, where it 

 is attached, to the distal end of the buccal retractor, where it is inserted. 

 In Cerion incanum the point of this insertion is in the center between 

 the right and left branches of the buccal retractor, while in the other 



