14 IOWA STUDIES IN NATURAL HISTORY 



Catoptometra and Eudiocrinus, both belonging to the Zygo- 

 metridae and both ranging from the IMalayan region to southern 

 Japan, which are definitely known to include both recent and 

 fossil species, it would seem that the Caribbean region has a 

 closer affinity with the past faunas than has any other area. 



The relative antiquity of the West Indian crinoid fauna seems 

 to be attested by the following facts : 



Of the 8 genera of stalked crinoids represented 4, or one-half, 

 occur also as fossils ; in the Indo-Pacific region out of 19 stalked 

 genera only 1 occurs as a fossil.* 



Of the 30 genera of comatulids 23, or 77%, include only five or 

 ten armed species. The Comasterinae, Himerometridae, 

 SxEPHANOMETRroAE and Mariametridae, including only multi- 

 brachiate species, are not represented; the Zygometridae, many 

 species of which are conspicuous for the great number of arms, 

 is also unrepresented. 



Of these 30 comatulid genera 23, or 77%, are monotypic, or 

 are represented by a single species. 



KEY TO THE GENERA OF CRINOIDS REPRESENTED IN THE 

 CARIBBEAN SEA AND ADJACENT WATERS 



ai No stem; the center of the dorsal side of the animal is occupied by a 

 single more or less thick plate or knob bearing jointed appendages by 

 means of which the animal attaches itself, 

 bi five very long and slender arms 



Pentametroerinus 

 b2 ten or more arms 



ci one or more of the proximal pinnules bears in its terminal por- 

 tion a comb-like structure formed by the production of the distal 

 outer side of each of the segments in the form of a long thin 

 triangular process 

 di more than ten arms 



el all of the division series are composed of two ossicles; 

 the lowest pinnule is on the second brachial following 

 the last axillary 



Neocomatella 

 e- first division series of two ossicles, the second of four of 



*Cf. The Ontogeny of a Genus, American Naturalist, vol. 45, No. 534, June, 1911, 

 pp. 372-374; The Comparative Age of the Recent Crinciid Faunas, American Journal 

 of Science [4], vol. 32 (whole No. 182), No. 188, August, 1911, pp. 127-132; Das 

 relative Alter der rezenten Seelilienfaunen, Naturwiss. Rundschau, JG. 27, No. 15, 

 April 11, 1912, pp. 191-192; On the Deep Sea and Comparable Faunas, Intern. 

 Revue der ges. Hvdrobiol. und Hydrogr., vol. 6, 1913, Heft 1, pp. 17-30, Heft 2/3, 

 pp. 133146. 



