[SCIENTIFIC RESULTS OF THE PHILIPPINE CRUISE OF THE FISHERIES 

 STEAMER "ALBATROSS," 1907-10.— No. 7.] 



THALASSOCRINUS, A NEW GENUS OF STiiLKED CRINOIDS 



FROM THE EAST INDIES. 



By Austin Hobart Clark, 



Assistant Curator, Division of Marine Invertebrates, U. S. National Museum. 



During the course of her investigations among the East Indian 

 islands, the United States Bureau of Fisheries steamer Albatross dredged 

 a small stalked crinoid which in certain important respects is different 

 from any hitherto known. It is evidently nearly related both to Hyo- 

 crinus and to Gej)hyrocrinus, and, with them, falls into the family 

 Hyocrinidse as redescribed by Koehlor and Bather, The affinities 

 appear to be closer to Gephyrocrinus than to Hyocrinus, and I was at 

 first inclined to consider it a new species of that genus. There is the 

 same curious elevation of the disk ambulacra from which that genus 

 derives its name, but the sides of this wall or bridge are completely 

 covered with perisomic plates. The basals are proportionately con- 

 siderably smaller than those of Gephyrocrinus, and their lower third 

 is cylindrical as in Hyocrinus, but they are not so elongated as in 

 that genus. They are three in number, the smaller being anterior 

 and the two larger lateral. Each bears at its base two tubercles, which 

 mark the angles of the stem; this latter is hexagonal proximally, 

 becommg slowly cylindrical; the upper columnars bear six tubercles, 

 marldng the angles ; on the lower cylindrical segments these tubercles 

 persist as short, small spines, resembling the condition seen in certain 

 species of Millericrinus. The arm bases do not occupy much more 

 than one-third of the distal edge of the radial, this form being there- 

 fore intermediate between Hyocrinus and Gephyrocrinus in this 

 feature. In Hyocrinus the first pinnule is on the sixth brachial (the 

 epizygal of the third syzygial pair) ; in Gephyrocrinus the first pinnule 

 is on the fourth brachial (usually the epizygal of the second syzygial 

 pair) ; in this new form it is on the fifth brachial, the epizygal of the 

 second syzygial pair, but the two first syzygial pairs are separated by 

 a single brachial. The orals and interambulacral plates are pierced 

 by about seventy water pores, which are not found, however, in the 

 interambulacral plates of the anal area. The orals are very large, 

 much larger than in either Hyocrinus or Gephyrocrinus and consist 

 of a broad triangular apex and a posterior portion, concave laterally 

 and posteriorly, which runs backward for some distance over the inter- 



Proceedings U. S. National Museum, Vol. 39— No. 1793. 



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