218 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



bears three spines (see fig. 17B); toward the mouth the two columns 

 diverge far more than one would assume from the original figure, and 

 in consequence there are long and slender syngnaths and not the 

 asterid-like mouthpieces figured in the illustration. (See fig. 17C.) 



3 



FIG. 17. DIAGRAMS OF T^NIASTEB SPINOSUS (BILLINGS). A, To SHOW THE SPINOSE DISK WITH CONCAVE 



SIDES. B, ACTINAL PLATE ARRANGEMENT: C, AMBULACRALS; ad, ADAMBULACRALS OR SIDE PLATES, 

 WITH THEIR SPINES. C, MOUTH PLATES: a, AMBULACRALS; S, SYNGNATH. 



The specimen of figures 3c and 3d is too poorly preserved to add 

 anything further. Associated with these types there is another and 

 much larger specimen with a well-marked disk, of which Billings 

 said nothing in his original description. This form is clearly of 

 another species (probably T. cylindricus) , and is mentioned here so 

 that other workers will not confound it with the original material 

 of T. spinosus. 



In 1900 Gregory referred Tseniaster to the asterid family Tsenias 

 teridse, and placed here as well the unrelated genera Stenaster, S alter- 

 aster, and Urasterella. From what has been stated above it is plain 

 that T&niaster can not be closely related to the cryptozonian genus 

 Urasterella , since the latter has an abundance of narrow ambulacralia, 

 asterid in type, while these ossicles in the former are far fewer in 

 number and of the form seen in other and related Lysophiurse. It 

 is very probable that Tseniaster -arose in the same stock that gave 

 rise to Urasterella and Stenaster, but the former genus is clearly one 

 of the aulurids. 



In 1896 Gregory took out of T&niaster the second species of 

 Billings (T. cylindricus) and based on it the new genus Tseniura. 

 As will be seen, this name can have no standing, as the generic char- 

 acters are those of Tseniaster, and, further, the name is preoccupied 

 since 1837. 



Thinking T. cylindricus most closely related to the primitive 

 ophiurids PalseopTiiura and St&rteura, Gregory defined T&niura as 

 follows : 



"Diagnosis: Palseophiuridse with a small pentagonal disk, not 

 bounded by marginal ossicles. The ambulacral furrow is broad. 

 The oral skeleton is conspicuous and the syngnaths each composed 

 of two separate pieces. The two jaws of each oral angle are closely 

 attached; the mouth frames are separated, and each of them is a 

 short, thick, slightly bent bar." 



