A MONOGRAPH OF THE EXISTING CRINOIDS 185 



segments increase in length as their number increases. On a detached arm fragment 

 there are pinnules 5 mm. long with 10 segments. The arrangement of the pinnules 

 resembles that in Th. latipinna. 



Notes. — Professor Koehler said that this species is most closely related to Th. 

 echinata from which it is distinguished by the less numerous cirri with less numerous 

 segments. The brachials are shorter with the distal border thickened forming a trans- 

 verse crest which bears only a few very fine spines. Although strongly developed, 

 Pi bears only a few very fine and scattered spinules which are invisible to the naked eye. 



Locality. — Princesse-Alice station 1713; off the southeastern coast of Tenerife, 

 Canary Islands (lat. 28°04' N., long. 16°49'30" W.); 1,330-1,340 meters; August 1, 

 1904 [Koehler, 1909; A. H. Clark, 1911, 1918, 1923;Mortensen, 1927] (1, Monaco Mus.). 



History. — Prof. Rene Koehler described and figured Antedon omissa in 1909 from a 

 single specimen in rather poor condition that had been dredged by Prince Albert I of 

 Monaco's yacht Princesse-Alice in 1904 at station 1713. 



In a paper on the crinoids of the AfricaD coasts published in 1911 I included Thalas- 

 sometra omissa and gave the range. In my memoir on the unstalked crinoids of the 

 Siboga expedition published in 1918 omissa was included in the key to the species of 

 Thalassometra and the synonymy and range were given. In my memoir on the crinoids 

 of the Ingolj expedition published in 1923 omissa was included in the key to the Atlantic 

 species of Thalassometra, and the range was given. Dr. Th. Mortensen in his handbook 

 of the echinoderms of the British Isles published in 1927 included a notice of Thalas- 

 sometra 07nissa. 



THALASSOMETRA sp. 



Thalassometra pergracilis (part) A. H. Clark, Crinoids of the Indian Ocean, 1912, p. 207; Unstalked 

 crinoids of the Siboga Expedition, 1918, p. 170. 



Locality. — Investigator; about 30 miles west of Middle Andaman; about 887 meters 

 (485 fathoms) [A. H. Clark, 1912, 1918] (1, I. M.). 



Remarks. — Regarding this individual I wrote in 1912: 



One mutilated specimen, agreeing well with Carpenter's description and figures. The centrodorsal 

 is rounded conical, 4 mm. broad at the base and 3 mm. high; the cirrus sockets are arranged in ten 

 columns, two to each radial area, those of each radial area being separated interiorly by a rather strong 

 ridge, exteriorly in close apposition with the columns of adjacent radial areas; the dorsal pole is rough, 

 covered with irregular tubercles; the disk is almost entirely covered with small rounded concretions; 

 the disk ambulacra are bordered with similar, but somewhat smaller and more thickly set, plates which 

 become radially elongated about the mouth; the perisome of the arms is covered with small round 

 concretions, and the interbrachial perisome with large fiat plates. 



In 19181 wrote that I was convinced that this specimen does not in reality represent 

 Th. pergracilis (^gracilis), and that it is in too poor condition for definite determination. 



Genus HORAEOMETRA A. H. Clark 



Antedon (part) von Graff, Bull. Mus. Comp. Zool., vol. 11, No. 7, 1883, p. 133, and following authors. 



Thalassometra (part) A. H. Clark, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 360. 



Cosmiometra (part) A. H. Clark, Unstalked crinoids of the Siboga-Exped., 1918, p. 154. 



Horaeometra A. H. Clark, Unstalked crinoids of the Siboga-Exped., 1918, p. 160 (only included species 

 H. duplex [P. H. Carpenter]) ; Univ. Iowa Studies in Nat. Hist., vol. 9, No. 5, 1921, p. 12 (confined 

 to the West Indies), p. 19 (in key) ; The Danish Ingolf-Exped., vol. 4, No. 5, Crinoidea, 1923, p. 

 40 (range). — Gisl£n, Kungl. Fysiogr. Sallsk. Handl., new ser., No. 11, 1934, p. 18. 

 843803—50 13 



