NO. 3 CASSIDULOID ECHINOIDS — KIER 21 



by the occurrence of almost all the living species in tropical waters 

 and of most of the Tertiary species in rocks believed to have been 

 deposited in tropical seas. According to Durham (1959, p. 9) the 

 Paleocene-Eocene tropical zone was much broader than it is today, 

 gradually contracting since the Eocene. This contraction may explain 

 the decrease in the cassiduloids, not only because it r«duced the area 

 where they lived, but also because it may have increased the compe- 

 tition between them and other animals occupying a similar niche. 

 It is probably significant that the great decrease in the number of 

 cassiduloids occurred at the same time as an increase in the number 

 of spatangoids and clypeastroids. 



ECOLOGY 



Unfortunately, the ecology of none of the recent species of cassid- 

 uloids has been studied. The only information of any significance 

 is A. Agassiz's (1873, p. 555) statement that Rhyncholampas pacifi- 

 cits (Agassiz) "lives like other spatangoids of which the habits are 

 known, gregariously on sandy beaches, from five to six feet below 

 low-water mark, half buried in the sand up to the extremities of the 

 petals." I have tried to locate in the Western Hemisphere a living 

 population of cassiduloids that I could study, but with no success. 

 Cassidulus cariboearum Lamarck lives in the Caribbean, but neither 

 I nor any of the many marine biologists that I have contacted have 

 seen them in any numbers. Dr. Lowell P. Thomas at the Marine 

 Laboratory at the University of Miami reported (personal com- 

 munication) that he had found one live specimen of C. cariboearum 

 on a sandy bottom in about 18 inches of water at Lameshur Bay, 

 St. John, Virgin Islands, but no observation was made on whether 

 the specimen was bufied or not. Fred Ziesenhenne reports (personal 

 communication) that he dredged up from 10 fathoms over 100 

 specimens of Rhyncholampas pacificus 175 miles northeast of Cape 

 San Lucas, Baja California, Mexico. These specimens came from 

 a sandy bottom, but Mr. Ziesenhenne could not observe how they 

 lived because of the depth of the water. He states that he has never 

 taken them in tangles, which would indicate that they do not live on 

 the surface of the sand. Other than this information, nothing is 

 known of tke living habits of the cassiduloids. It is hoped that some- 

 one will make a study of the cassiduloids similar to the magnificent 

 work done by Nichols (1959) on the spatangoids. 



From a study of the morphology of the cassiduloids it can be 

 conjectured that they lived only partially buried up to their petals. 



