THE NAUTILUS. 9 



length, (bullaform) they come up to the mangrove roots that fringe 

 the coral islands. These islands, or keys, are half surrounded, on 

 the sheltered side, by clear channels two or three feet deep. These 

 channels have free communication with the sea. The favorite food 

 for exanthema is washed in from the live coral beds by every tide. 

 The mangroves furnish shelter and coloring matter for the shell- 

 Exanthema, unless disturbed does not leave the mangroves till ready 

 to breed, when it goes to deeper waters. Cypraea exanthema is 

 elongated, cylindrical, with tapering extremities, anterior aperture 

 narrow and not depressed. The head and neck of animals is small, 

 not often extended, because food comes to it. Sides of shell profusely 

 decorated with ring spots, particularly near the base. Spots white 

 with dark centers. The mantles, in young shells are purple black, 

 studded with pustules that project flexible papillae. These papillae 

 may be extended or withdrawn entirely into the pustule. The 

 pustules become transparent lenses as the shell approaches adult 

 form. The papillae remain black and receive color through a circu- 

 lation duct that is easily visible to the naked eye, particularly where 

 it crosses the lens to the papilla. The lenses form the spots and 

 the papillae form the central dots. These papillae are loaded with 

 color and probably deposit all the color needed for decoration of the 

 outer shell. The inner mucous membrane supplies the enamel. 

 The papillae near the outer edge of mantle soon lose the color bear- 

 ing faculty, or, lacking supply, produce only nebulous white spots 

 near the top of the shell. These papillae possess a highly sensitive, 

 independent, nerve ganglia. If one be touched, however delicately, 

 it will instantly be withdrawn. The others will not be disturbed. 



Color of shell, fugitive purple that turns to shades of brown upon 

 exposure to light. Length of shell three to four inches, altitude 

 about one-third the length. 



C. exanthema is found on both sides of the Gulf Stream which is a 

 thousand feet deep between Florida and the Bahamas, with a current 

 of five or more miles an hour. Bahama, Jamaica and Colon 

 specimens are coarser in texture, the spots are less frequent, form 

 less regular and the color much paler. Less food and fewer man- 

 groves. The true exanthema is not found on the Florida west 

 coast. 



CYPRAEA CERVUS. The most favorable habitat of this shell is 



