A MONOGRAPH OF THE EXISTING CRINOIDS 255 



Cyllometra impinnata A. H. CLARK, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 357 (listed); 

 Proc. Biol. Soc. Washington, vol. 22, 1909, p. 6 (listed). 



Characters. Cirri VIII-X, 12. P, P 2 , and P b absent. 



Remarks. Carpenter said that this is a little species, which was obtained at 

 Mauritius by Professor Mobius, who was kind enough to show it to him when he visited 

 Kiel. The only characters he gave for it are those given above. 



When the genus Clarkometra was described I believed that Carpenter's Antedon 

 impinnata might be a representative of it, related to or possibly identical with the type 

 species, C. elegans, and I so wrote to Dr. Gisle"n. But he pointed out that Carp enter 

 said nothing about PI in Antedon impinnata, so that, therefore, this pinnule is pre- 

 sumably present. He believes that "Antedon impinnata" is simply a young individual 

 of some larger species, and on the basis of the available facts I quite agree with this 

 conclusion. 



Locality. North Bay, Mauritius; 27 meters; Prof. Karl Mobius [von Graff, 

 1884; P. H. Carpenter, 1888; A. H. Clark, 1907, 1909, 1911, 1912; Gislen, 1922.]. 



History. Antedon impinnata was first mentioned by Prof. Ludwig von Graff 

 who in 1884 described the myzostomes found upon the only known specimen. The 

 myzostomes and the name of the host had been sent him by Dr. P. H. Carpenter. 



In the Challenger report upon the comatulids published in 1888 Carpenter in- 

 cluded Antedon impinnata in a key to five 10-armed species that did not seem to fit 

 into any of the specific groups established by him. 



In my first revision of the old genus Antedon published hi 1907, I placed impin- 

 nata in the new genus Cyllometra, and it was listed as a species of Cyllometra in my re- 

 vision of the family Himerometridae published in 1909. In my memoir on the crin- 

 oids of the coasts of Africa published in 1911, I listed Antedon impinnata as an un- 

 identifiable species and gave the characters mentioned by Carpenter. It was similarly 

 included in the list of unidentifiable species under the name Antedon impinna'a in my 

 memoir on the crinoids of the Indian Ocean published ha 1912. 



In 1922 Dr. Torsten Gisl6n pointed out that Antedon impinnata is probably merely 

 a young individual of some other species. 



Superfamily TROPIOMETRIDA A. H. Clark 



Thalassometroida A. H. CLARK, Amer. Nat., vol. 42, No. 503, 1908, pp. 722, 723 (includes Thalas- 



sometra, Charitomelra, Tropiometra, and other genera) . 

 Thalassometrida GISL^N, Zool. Bidrag Uppsala, vol. 9, 1924, pp. 231, 236, 237, 238, 239, 240; Ark. 



Zool., vol. 19, No. 32, 1928, p. 6. SIEVBHTS, Neues Jahrb. Min., Geol. und Pal., vol. 69, Beilage- 



Band, Abt. B, 1932, p. 151. GISLN, Kungl. Fysiogr. Sallsk. Handl., new ser., No. 11, 1934, 



p. 7. 

 Tropiometrida A. H. CLARK, Rec. Indian Mus., vol. 34, pt. 4, 1932, p. 560; Treubia, vol. 14, livr. 2, 



1933, p. 213; John Murray Exped. 1933-34, Sci. Reports, vol. 4, No. 4, 1936, p. 90. H. L. 



CLARK, Mem. Mus. Comp. Zool., vol. 55, 1938, p. 42. 



Diagnosis. A superfamily of the suborder Oligophreata hi which all the pinnules 

 are prismatic, triangular in cross section, with a sharp, or sharply rounded, dorsal 

 keel; well-developed side- and covering-plates are usually, though not always, present 

 along the pinnule ambulacra; the arms terminate abruptly, the minute terminal 

 brachials being curved inward between the fully developed terminal pinnules, which 

 extend for some distance beyond them; all the pinnules are present in all the species. 



