ISCHNOCHITON. 81 



Islands of St. Paul and Amsterdam (French Transit of Venus 

 Exped., 1874). 



Chiton constanti VELAIN, 1. c., p. 124, t. 4, f. 21, 22. 



This species is abundant throughout the littoral zone of both 

 islands, especially within the crater of St. Paul, where it covers some 

 rocks. 



I. CESSACI Rochebrune. PL 10, figs. 13, 14, 15, 16, 17. 



Shell ovate-oblong, subcarinated, painted with various colors. 

 Anterior valve and posterior area of the posterior valve lightly con- 

 centrically lineated, the lines most minute ; intermediate valves hav- 

 ing the central areas striatulate, strise interrupted ; lateral areas very 

 delicately undulated. Marginal ligament narrow, scaly. 



Length 18, breadth 8 mill. (Rochebr.) 



Strait of Santiago, Cape Verde Archipelago, (Cessac and Bouvier.) 



Lepidopleurus cessaci ROCHEBR., Bull. Soc. Philom. 1881, p. 118 ; 

 Nouv. Arch, du Mus. (2) iv, p. 241, t. 17, f. 11, a-e. Leptochiton 

 cessaei ROCHEBR., Journ. de Conch. 1881, p. 43. 



This species is evidently allied to J. rissoi Payr. 



In the great number of specimens from Cape Verde and the whole 

 west coast of Africa (Bank of Argain, Dakar, Goree, Rufisque and 

 Madeline Is.), twelve color varieties are found, as follows. 



1. Greenish yellow with a brown median line, mantle white. 



2. Deep yellow orange ; mantle light yellow. 



3. Dark brown with a white median line ; mantle gray. 



4. Dark violet ; mantle blue. 



5. Light violet ; marbled with white ; mantle rose. 



6. Olive ; mantle white or black. 



7. Uniform gray ; mantle blue. 



8. Gray-white ; mantle orange. 



9. Gray marbled with orange ; mantle violaceous. 



10. Rose ; mantle gray. 



11. Rose, marbled with green; mantle yellow. 



12. Finely marbled with red, blue, yellow on a gray or rose ground. 



I. RUGULATUS Sowb. (Vol. XIV, p. 110.) 



The name was spelled " regulatus " in the text, by typographical 

 error. 



