A MONOGRAPH OP THE EXISTING CRINOIDS 5 



protecting roof over the gonads. The genus Horaeometra is confined to the Caribbean 

 Sea, occurring in water of from 159 to 479 meters in depth. 



History. In Dr. P. H. Carpenter's Challenger Report published in 1888 the species 

 of the family Thalassometridae known to him were distributed among the Basicurva, 

 Spinifera, and Granulifera groups of the genus Antedon. The family Thalassometridae 

 was established in 1908 to include the genera Thalassometra, Poecilometra, and Chari- 

 tometra, the genus Stylometra being added later in the same year. In January 1909, 

 the family Thalassometridae was divided into the subfamilies Thalassomctrinae, in- 

 cluding the genera Stylometra, Thalassometra, Stenometra, Stiremetra, Parametra, and 

 Cosmiometra, all but the two first new, and Charitometriuae, the equivalent of the family 

 Charitometridae as now understood. 



In 1911 the subfamily Thalassometrinae was raised to family rank and Ptilometra, 

 Pterometra, and Asteromctra were transferred to it from the family Tropiometridae. In 

 1914 the family Thalassometridae was divided into the two subfamilies Ptilometrinae, 

 including the genera Ptilometra, Pterometra, and Asterometra, and Thalassometrinae, 

 including the remaining genera. In 1934 Prof. Torsten Gislcn raised the subfamily 

 Ptilometrinae to family rank, leaving the family Thalassometridae as herein understood. 



KEY TO THE GENERA OF THE FAMILY THALASSOMETRIDAE 



a 1 . Genital pinnules with no appreciable expansion of earlier segments. 



6 1 . Arms, at least in outer portion, laterally compressed and sharply carinate, the carination pro- 

 duced into a high crest or broad overlapping spine; arms more than 10 (or by individual 

 variation 10) in number, the division series all 2; PI longer and proportionately stouter than 

 P 2 , though not otherwise different. 



c 1 . Division series and arm bases narrow and laterally compressed, gablelike in cross section like 

 the outer brachials, the carination of the outer brachials being continued proximally to 

 the centrodorsal; cirri long and slender. 



d l . Arms 20 in number, 65-100 mm. long in fully developed individuals (from Timor and the 

 Moluccas north to the Boniu Islands and southern Japan; 141 [?95]-457 meters). 



Stenometra (p. 7) 



(P. Arms 10-18 (usually 10-15) in number, usually 60-65 mm. long (from Port Denison, 

 Queensland, to Timor and north to southern Japan; 22-548 meters). 



Daidalometra (p. 23) 

 c 1 . Division series and arm bases evenly rounded or more or less flattened dorsally, occasionally 



with a slightly raised middorsal line. 

 d l . Cirri long and slender with more than 35 segments; division series and lower brachials 



usually more or less spinous, or at least bordered with fine spines; 20-30 arms. 

 e 1 . Elements of the division series and lower brachials armed with numerous prominent 

 spines, at least along their borders; brachials beyond the proximal each with a long, 

 thin, broad, and prominent curved overlapping spine (Caribbean Sea; 102-508 [?548] 



meters) Stylometra (p. 29) 



e 2 . Elements of the division series and lower brachials smooth or with bands of minute 

 spines along their borders; carination of the brachials not produced into overlapping 

 spines (from southern Japan and the Hawaiian Islands to southeastern Australia and 

 westward to Ceylon, the Maldivo Islands, -and Saya de Malha; 183 [?12S]-730[?740] 



meters) Cosmiometra (p. 41) 



d 2 . Cirri shorter and stouter with not more than 35 segments; division scries and lower bra- 

 chials smooth, or with the lateral borders roughened or coarsely granular. 

 e 1 . Cirri with at most 27 (usually 20-25) segments, short and stout; division scries and arm 

 bases well rounded dorsally, appearing narrow and only slightly flattened against their 



