1896.] OF TUB palL Eozoio opmnnoiDBA.. 1035 



form of narrow bars ; also by the absence of the strong marginal 

 plates round the disc. The genus contains two species, S. brisin- 

 c/oides (Greg.) and S. leptosoma (Salt.) [13. p. 331, pi. ix. fig. 5], 

 both of which were originally placed in Frotaster. 



The genus differs from Protasler by the family character of 

 having bar-shaped instead of boot-shaped ambulacral ossicles. 



I have pleasure in naming this genus after Herr Stiirtz, whose 

 careful dissections have added so greatly to our knowledge of the 

 Pala;ozoic Ophiurids, and who has previously pointed out [17] that 

 these two species are generically distinct from Frotaster. 



Genua 3. T^niuka, uov. gen. 



Diagnosis. — Palajophiuridtc with a small pentagonal disc, 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. 



Bistrihution. — Trenton Limestone, Ottawa. 



I'ype species. — Tamiura cylindricus (Billings) [2. pp. 81-82, 

 pi. X. figs. 4 a, 4 h'\. 



Remarlcs. — This genus differs from Palceopliiura by the absence 

 of marginal ossicles from the disc, and from Sturtzura by the 

 smaller size of the disc and the form of the syngnaths. In 

 Sturtzura the jaws end bluntly against a jaw-plate, whereas in 

 Tamiura they appear to taper to a point and have no jaw-plate. 



This genus is necessary for the second species included by 

 Eillings in his genus Taniaster. The genus was described as disc- 

 less, which in respect to the type species S. sjnnosus is correct. 

 In that species the oral skeleton consists of five pairs of large 

 adambulacrals as in ordinary Asterids. The affinities of the true 

 Tmniasier appear to me to be with such forms as Palceaster 

 ruthveni (Forbes) [4. dec. 1, pi. i. fig. 1]. It is asteroid in the 

 oral armature, in its alternately arranged ambulacral ossicles \ and 

 in the absence of a disc. I therefore consider Taniaster a genus 

 of Asteroidea. The second species placed by Billings in this 

 genus has, however, a well-marked disc '\ and has the oral arma- 

 ture composed of five pairs of Ophiuroid syngnaths. It must 

 therefore be included among the Ophuiroidea. 



Genus 4. Etoaster, Hall, 1867 [6. p. 290, pi. ix. figs. 7, 8]. 



Diagnosis. — PalaBophiuridse in which the ambulacral ossicles are 

 subheptagonal in form, the central suture along the arm being 

 zigzag, while the outer augles of the ossicles are cut away for the 



1 Billings in his description (2. p. 81) attributes the alt;ernntion of llio 

 ossicles ill 2'<sniaster spinosiis to distortion ; but tliia explanation is not con- 

 sislont with his figure. If distortion had separated the pairs of ambulacral 

 ossicles it onglit also to have displaced the syngnaths ; but those of each pair 

 are left precisely opposite. 



' Billings, op. cit. pi. x. fig. 4 a. 



