58 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



tion could have been caused by an injury near ocular I where new 

 plates are produced. The posterior genital plates, 5 and 1, have no 

 pores, but two large pores in ocular I presumably are the pores 

 normally found in those genital plates (pi. 16, fig. 3). 



CONCLUSIONS 



Echinoids studied here seem to show definite habitat preferences 

 that could provide significant clues to interpretation of conditions in 

 ancient seas by paleoecologists. Moreover, they could be valuable to 

 the modern ecologist or sedimentologist who retrieves samples by 

 dredge or trawl. For example, Clypeaster rosacens dredged from 

 clean sand would indicate that grassy areas were nearby, as grassy 

 sand is the preferred habitat of that species. In addition, the material 

 that this species carries on its back is a clear indication of the nature 

 of the bottom. Similarly, the paleoecologist who found a fossil of 

 this species or a species of similar shape, such as Clypeaster antillarum 

 Cotteau from the Tertiary of the Caribbean area, could infer the 

 presence of turtle grass on the former sea bottom. This in turn gives 

 an indication of limits of depth at which the Tertiary formation was 

 deposited, because this grass does not thrive much below 40 feet. 



Many of the species that live in the Coral Reef Preserve occur as 

 fossils, and others have near relatives that are known from Tertiary 

 and Quaternary formations. A fossil assemblage that contains 

 Lyiechinus voriegatus, with Arbacia punctulata (or similar A. im- 

 proccra (Conrad)) and Eucidaris tribidoides or a similar form, indi- 

 cates a sandy bottom with dense turtle grass, at depths as great as 

 40 feet, but relatively near shore. Admixtures of Clypeaster subde- 

 pressus, or the similar fossil C. sunnilandensis Kier, and some of the 

 thin sand dollars indicate patches of clean, grassless sand among the 

 turtle grass. 



Mconia vcntrkosa has not been reported as a fossil. However, 

 species similar to it in shape, such Rhyncholampas evergladensis 

 (Mansfield) which occurs in the Tamiami Formation of Florida 

 (Kier, 1963), probably had similar living habits. These forms indicate 

 a sandy bottom with little or no turtle grass, located relatively far 

 from shore. Likewise, a sandy, grassless bottom could be inferred 

 from presence of M. ventr'xcosa or similar forms in a dredge haul. 



Some species of regular echinoids seek rocky or reefy environ- 

 ments, where niches and rock slabs provide cover. All large Diadema 

 antillarum observed in the Coral Reef Preserve were on rocky sub- 



