346 Dr. J. TF. Gregory — On Palceozoic Starfishes. 



This is the third species referred by Mr. R. Etheridge, jun., to 

 Monaster, but he does not definitely choose any one of the three as 

 the type ; tlie name having been suggested " from the one or single 

 row of adainbulacral plates on each side of an ambulacral avenue." 

 M. giganteus is the best type ; for by adambulacral plates Etheridge 

 no doubt means all the actinal plates except the ambulacrals, as 

 the true adambulacrals are always uniserial. M. Strutchbnrii, 

 Eth., jun., is also a Monaster, but M. Clarlcei is referred to a new 

 genus (p. 353), 



Subfamily 2. XENASTERINiE. 

 Diagnosis. 



Paleeasteridge with the general characters of the Pala^asterince, but 

 with most of the ambulacral ossicles opposite. 



XENASTER, Simonowitsch, 1871. 

 "Aster, rhein. Grauwacke " : Sitz. k. Akad. Wiss. Wien, vol. Ixiv, p. 88. 



Type Species. — Xenaster margaritatus. Op. cit., p. 88, pis. i 

 and ii. Devonian : Germany. 

 Affinities. 



This genus has been assigned by von Zittel and Nicholson to the 

 Asteriai verge, owing to the opposite position of the ambulacral 

 ossicles, which is the main character of the subfamily to which the 

 genus is here referred. The iuterradial areas are larger than in 

 typical species of Paleeasteridse, at least in the type of Xenaster ; 

 but X. simplex, Sim., which ought no doubt to be made the type 

 of a new genus, agrees closely with characteristic forms of PalcBoster, 

 except in the opposite position of the ambulacral ossicles. The 

 value of this character is doubtful since in Simonowitsch's figure of 

 X. margaritatus on pi. ii, fig. 3, while some of the adambulacrals 

 are opposite, others are alternate ; probably the ambulacral ossicles 

 would vary in the same way. If it should appear on re-examination 

 of the types of the genus that Simonowitsch's figures (e.g., his pi. i, 

 fig. 1& ; pi. iii, fig. Ih) are incorrect, then the subfamily would be 

 unnecessary, and Xenaster simplex might enter Palceaster, and 

 X. margaritatus take rank close to Palceaster eiicharis. Hall, for 

 which otherwise a new genus is wanted. 



Subfamily 3. LINDSTROMASTERIN^. 

 Diagnosis. 



Palasasteridee with alternate ambulacral ossicles, a large disc 

 covered with tessellate plates, and large interradial areas. 

 1. LINDSTROMASTER, nov. gen. 

 Diagnosis. 



Palseasterinid^ with flat pentagonal disc and five short blunt rays. 

 The plates of the disc are large, polygonal, tuberculate, and 

 crowded into a close tessellate pavement, which completely 

 covers the interradial areas. 

 Marginal plates well developed and conspicuous, and but slightly 

 smaller than the adambulacrals. Both supra- and infra- 

 marginals appear to be present. 



