6 PROCEEDINGS OF THE NATIONAL, MUSEUM. vol.65. 



far described to 51 species, distributed among 31 genera, of which 

 12 species, belonging to 8 genera, are of the stalked type.^** 



The crinoids existed in the Mesozoic in great profusion, their fossil 

 remains having been found to the number of upward of 400 de- 

 scribed species, belonging to more than 40 genera, many of them per- 

 fectly preserved and some of cosmopolitan distribution; while in 

 contrast to the scant 40 species known from the Tertiary there are 

 now described from existing seas 576 species of crinoids, belonging 

 to 142 genera, of which 76 species, of 22 genera, are of the stalked 

 variety. The question naturally arises, what became of the crinoids 

 in the meantime ? 



The scarcity of crinoids in the Tertiary, and the fragmentary con- 

 dition of their remains, is indeed surprising when compared with 

 their relative abundance in the Jurassic and Cretaceous and also in 

 the recent seas. And yet if the present reefs and beaches vrere 

 known onh' in a fossil condition we should find exactl}^ the same 

 state of afiairs. 



The marine Tertiarj' sedimentaries are composed chiefly of littoral 

 and reef materials, laid down in shallow seas. The fossils which 

 abound in them belong mostl}' to organisms of which the hard parts 

 are firmly constructed and capable of enduring the effect of shore 

 action. The crinoids of Cenozoic time, on the other hand, are 

 delicately organized and of fragile construction, so that with a few 

 exceptions like HoJopus they are broken up with the least disturb- 

 ance. 



When a comatulid dies — and comatulids are extremely sensitive — 

 it at once disintegrates, and the only recognizable portion that re- 

 mains is the radial pentagon with the controdorsal, or either of the 

 two alone. 



The reefs of to-day support a crinoid fauna of approximately 245 

 species, all of the comatulid type. Most of these are very local, 

 occurring only in a few limited regions, and many are very rare. 

 In the Caribbean region, w^iere in the deeper waters crinoids are 

 often abundant, the shore line records are : 



Nemaster grandis A. H. Clark: "Mexico," 1758. Nemnster iowen- 

 sis (Springer): Tortugas, 1893; Bahamas. Antedon duhenii 

 Bohlsche : St. Thomas, about 1850. Cenocrinus asteria (Linnaeus) : 

 Barbados, about 1870. Holopus rangii D'Orbignj^: Barbados, 6 

 records; ? Bermuda. Democrinv^ rawsonii (Pourtales) : Guade- 

 loupe. 



A recent reef if fossilized might show, as extremely rare objects 

 confined to a very few closely circumscribed localities, the radial 



'« See Austin H. Clark, 1921. Report on the Crinoids collected by the Barbados- 

 Antigua Expedition from the University of Iowa, in 1918. University of Iowa studies in 

 Natural History, vol. 9, No. 5, pp. 12-14. 



