REVISION OF PALEOZOIC STELLEKOIDEA. 217 



that species which I have named Protaster forbesi, the proportions of 

 plates and relations of parts showing specific differences/' 



"Mr. Billings remarks, under the description of T. spinosus, that 

 ' the ambulacral ossicles appear in some places to alternate with each 

 other, but this is owing to a distortion; those on one side of the furrow 

 are opposite to those upon the other. 7 



"Now the specimen of this species which I have examined, and 

 which I suppose to be the one figured upon Plate X, figures 3d, Z>, 

 has the ambulacral plates alternating * * *. 



"In the specimen of T. cylindricus examined the ambulacral 

 plates are less distinctly alternate, but the relation of the adam- 

 bulacral plates and the pores are the same as in the other form. 

 Not having seen the specimen showing the dorsal view, figure 4o- of 

 plate X, I can only remark that the structure of the rays is very 

 similar to that of Protaster." 



Without restudying the type-material of Tseniaster, or paying 

 attention to Hall's statements that T. spinosus has what he con- 

 ceived "to be a disk not at all unlike the disk of Protaster," Gregory 

 (1897) regarded Tseniaster as a Cryptozonia starfish and made of 

 Billings's second species, T. cyliiidricus, a new genus, Tseniura. The 

 latter he correctly refers to the primitive ophiurids. Under these 

 circumstances it is desirable to repeat here what Gregory wrote 

 about Tseniaster. 



Tseniaster "was described as diskless, which in respect to the type 

 species T. spinosus is correct. In that species the oral skeleton 

 consists of five pah's of large adambulacrals, as in ordinary Asterids. 

 The affinities of the true Tseniaster appear to me to be with such forms 

 as Palssaster ruthveni [= Urasterella ruthveni]. It is asteroid in the 

 oral armature, in its alternately arranged ambulacral ossicles, and in 

 the absence of a disk. I therefore consider Tseniaster a genus of 

 Asteroidea. The second species placed by Billings in this genus 

 has, however, a well-marked disk, and has the oral armature com- 

 posed of five pairs of Ophiuroid syngnaths. It must, therefore be 

 included among the Ophiuroidea." 



To adjust this matter, the writer restudied the genotype of Tseniaster 

 at Ottawa (two specimens, No. 1404, the originals of figures 3a-3d 

 of Billings's Plate X). There can be no doubt that we have here a 

 genuine lysophiurid. There is a small disk present in the individual 

 figured as 3a and 3Z>, but it is not one with a round outline, as in 

 typical ophiurids, but is concave along the margin between the rays. 

 Actinally this disk is abundantly covered with prominent but slender 

 spines. 



The ambulacrals are distinctly alternate throughout the rays and ap- 

 pear as in the sketch presented on page 218; this condition is not due 

 to distortion or other causes. The side plates are narrow, and each 



