A MONOGRAPH OF THE EXISTING CRINOIDS 161 



dial pentagon shows traces of a basal star. On the articular faces of the radials the 

 muscular fossae are of about the same size as the interarticular ligament fossae, and 

 have a smooth surface. 



The ambulacral plating of the pinnules is composed, according to Hartlaub, of 

 side- and covering-plates. The latter are fine-meshed approximately oval plates. 

 They rest on the side plates and are apparently movable, since their position is vari- 

 able. Sometimes they he flat like imbricating tiles, and sometimes they are more 

 raised. If they are viewed from below when in this position it is seen that they have 

 an alternating oblique position in reference to the longitudinal axis of the arm. Then- 

 precise attachment was not determined by Hartlaub. They are exceedingly small, 

 very brittle, and difficult to isolate. They are attached by ligaments that are not 

 broken down by boiling for several minutes in caustic potash, and too long boiling in 

 caustic destroys them. The side plates are arranged in a zigzag. On each side of 

 the ambulacral groove they form a sort of Spanish wall. In the niches of this wall, 

 more or less concealed, lie the sacculi. The produced angles are mostly formed by two 

 apposed plates; in other places, for instance at the end of a pinnule, they appear to 

 originate from breaking off from a single plate. The side plates are more wide-meshed 

 than the covering plates and are often quadrangular with notched edges. In certain 

 places one sees that through these regularly recurring notches two gaps are formed 

 in the line of contact of their ends. The higher gap is occupied by a sacculus and 

 through the lower a tentacle protrudes. 



Localities.- — Albatross station 3409; Galapagos Islands (lat. 0°18'40" S., long. 

 90°34'00" W.); 598 meters; bottom temperature 5.7° C; black sand; April 3, 1891 

 [Hartlaub, 1895; H. L. Clark, 1902; A. H. Clark, 1907, 1909, 1912, 1918]. 



Albatross station 3408; Galapagos Islands Gat. 0°12'30" S., long. 90°32'30" W.); 

 1,250 meters; bottom temperature 4.2° C; globigerina ooze; April 3, 1891 [Hartlaub, 

 1895; H. L. Clark, 1902; A. H. Clark, 1907, 1909, 1912, 1918]. 



Albatross station 3357; off Mariato Point, Panama Gat. 6°35'00" N., long. 

 81°44'00" W.); 1,429 meters; bottom temperature 3.6° C; green sand; February 24, 

 1891 [Hartlaub, 1895; H. L. Clark, 1902; A. H. Clark, 1907, 1909, 1912, 1918]. 



Geographical range. — From the Galapagos Islands to Panama. 



Bathymetrical range. — From 598 to 1,429 meters. 



Thermal range.— From 3.6° to 5.7° C. 



History. — Antedon agassizii was described and figured by Dr. Clemens Hartlaub 

 in 1895 from specimens from Albatross stations 3408 and 3409 in the Galapagos Islands 

 and station 3357 off Mariato Point, Panama. Hartlaub did not give the number of 

 specimens he had, but mentioned three from station 3408 that apparently were not 

 included in the original description. He described and figured the centrodorsal and 

 radial pentagon, and the side- and covering-plates, and discussed the relationships of 

 the species in detail. Dr. Hubert Lyman Clark in 1902 listed Antedon agassizii among 

 the echinoderms known from the Galapagos Islands. 



In my revision of the genus Antedon published in 1907 agassizii was transferred to 

 the new genus Thalassometra, and in my revision of the family Thalassometridae 

 published in 1909 it was listed as Thalassometra agassizii. In my memoir on the 

 crinoids of the Indian Ocean published in 1912 and again in my report on the unstalked 

 crinoids of the Siboga expedition published in 1918 Thalassometra agassizii was listed 



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