(jhrotts Anatomy of Campeloma. 497 



above the base of the left tentacle. The chamber is somewhat less 

 in size in the gravid female than in the male, a fact the explanation 

 of which probably lies in the distension of the gestatory sac and 

 its consequent encroachment upon the branchial space. The cham- 

 ber narrows rapidly posteriorly, and becomes laterally constricted. 

 From its upper and left side walls is pendant the ctenidium 

 (Plate ? Fig. 5, Br). This organ consists of a single row, contain- 

 ing a great number of thin elongately triangular plates, connected 

 above with the branchial vein. The right edge and lower extrem- 

 ity of each plate is free, and each is constantly bathed with water. 

 The plates become smaller as the rear end of the chamber is reached; 

 they are yellowish white in color, and are furnished with abundant 

 cilia. The blood, which is aerated in these plates, is white. 



The attention of students with proper appliances at command is 

 directed to these molluscs in respect to their embryology, nervous 

 system, minute anatomy of the reproductive organs, myology and 

 circulatory system. Only the crudest observations on these points 

 were possible under the conditions which were presented to me, and 

 such facts as were ascertained are repressed in the hope that some 

 other one will be able to complete the work here outlined. 



Explanation of the Plate. X f. All the figures, save Fig. 2, 

 are drawn from the female. The mantle is clipped along the left 

 margin of the branchial cavity. 



Fig. 1. Female, Fig. 2, male individual. 



Fig. 3. A single transverse row of teeth. 



Fig. 4. Odontophore, natural size and very greatly enlarged. 



Fig. 5. Anatomy of the branchial cavity with related organs. 



a. Rectum and anus. 



b. The opening of the gestatory sac, c. 

 br. The ctenidium. 



The figures on the plate were drawn by Mr. H. A. Pilsbry 

 from dissections made by him. Those in the text are drawn, some 

 what diagraminatically, by the author, from nature. 



