444 PROCEEDINGS OF THE ACADEMY OP [1898. 



Row 3. Exterior views of dwarfs (mature females) 

 from interior of Illyonassa and Littorina shells 

 inhabited by the small hermit crab. 



Row 4. Interior views of same. Last five shells in 

 row males and immature forma of dwarfs. 



Plate XXIII. All shells shown are those of C. plana. 



Row 1. Immature forms; not differentiated sexu- 



ally- 

 Row 2. Mature males. 

 Row 3. First six, mature males ; seventh to tenth, 



forms intermediate between males and females; 



last shell in row immature female. 

 Row 4. Mature females ; a few with males attached. 



