138 University of Michigan 



PLATE XI 



The scales of figs. 40 and 41 represent a length of 50 microns (.05 

 mm.), while those of figs. 42 to 47 indicate one millimeter. 



Fig. 40. Tudora maculata. Central and laterals; radula from B4. 

 Also outer lateral in profile; lateral view. 



Fig. 41. Tudora muskusi rmisTcusi. Central and laterals; radula 

 from CI 7b. 



Fig. 42. ' Cistulops raveni. Exterior surface of operculum; from C5c. 



Fig. 43. Tudora muskusi muslcusi. Exterior surface of operculum; 

 from C17b. 



Fig. 44. Tudora pilsiryi. Exterior surface of operculum; from C2a. 



Fig. 45. Potamopyrgus parvulus. Large, globose form, from Bel. 



Fig. 46. Potamopyrgus parvulus. Elongate form, from Kcl. 



Fig. 47. Potamopyrgus parvulus. Spinulose form, from Kcl. 



