300 TWENTIETH REPORT ON THE STATE CABINET. 



SUPPLEMENTARY. 



NOTE ON THE GENUS T^NIASTER (Billings). 



The Genus T^niaster is thus described : 



" Generic characters. Body deeply stellate ; no disc or marginal plates ; 

 " rays long, slender, flexible, and covered with small spines; two rows 

 " of large ambulacral pores; adambulacral plates elongated and sloping 

 " outwards, so that they partly overlap each other : adambulacral ossi- 

 " cles contracted in the middle, dilated at each end." 



Mr. Billings remarks that this genus differs from Protaster ( as 

 described by Mr. Salter in the Annals and Magazine of Natural History, 

 Nov. 1857) in the following particulars : 



" 1. Protaster has a well developed disc; '* 



" 2. It has also the pores outside of the ambulacral ossicles [see Mr. 

 Salter's fig. 40 in the article above citedj ;" 



" 3. The same figure shows that the oral plates of P.miltoni are formed 

 of two of the ambulacral ossicles, instead of two of the adam- 

 bulacral plates." 



In reviewing the characters of Protaster and Eugaster, I became 

 satisfied that there was an intimate relation between these and T^niaster 

 of Billings ; and in order to satisfy myself on this point, I have, since 

 the preceding pages were printed, requested, and kindly received from Sir 

 William E. Logan, permission to examine specimens of Tceniaster spino- 

 sus and T. cylindricus ( Decade iii, Canadian Organic Bemains, Plate x, 

 figures 3 and 4). 



An examination of the specimen illustrated in fig. 3 (ut sup.) reveals 

 what I conceive to be a disc not at all unlike the disc of Protaster, but 

 less extended than in the Lower Helderberg species. The structure of the 

 ray is precisely of the same character as the ray of that species which I 

 have named Protaster forbesi, the proportions of plates and relations of 

 parts showing specific differences. 



It is true that the figure of Mr. Salter represents the oral ossicles as 

 proceeding from the ambulacral plates ; a feature which I think can scarcely 

 exist, and the representation is probably due to an oversight, or to a distor- 

 tion of the specimen. I believe, moreover, that on examination of more 

 perfect material, Mr. Salter will ascertain that the position of the pores 

 is not precisely as represented. 



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

 " ambulacral ossicles appear in some places to alternate with each other, 

 " but thi'^ is owing to a distortion : those on one side of the furrow are 

 " opp^^ those upon the other." 

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