52 NEW YORK STATE MUSEUM 



are the same. The madreporite, however, which is oval and striate 

 as in the genotype, is smaller by one-sixth although the specimen is 

 larger by one-third. The ambulacral plates are distinctly opposite, 

 while in the specimen of P . gregoryi they are apparently 

 alternating, probably owing to oblique shoving of the entire starfish. 

 The plates themselves are alike in outline in both species ; they 

 have a spoon-shaped crest which in P . r'oemeri is narrower and 

 lacks the distinct widening at the inner end and is more sharply 

 bent, thus resembling a single right angle. The adambulacral plates 

 are smaller and less prominent than in the genotype. The ambulacral 

 groove which is very narrow in P . gregoryi is distinctly wider 

 in the other species. The spines which form a dense covering in 

 both species are for the main part simple and not compound as in 

 P. gregoryi, especially so on the disk. 



Stenaster salteri (Billings) 

 Plate ii, figures i and 2 



The State Museum contains a slab of Trenton limestone from 

 Kirkfield, Ontario, which bears two beautifully preserved specimens 

 of Stenaster salteri (Billings) that reveal some structures 

 hitherto not recognized. 



The two specimens present the abactinal or dorsal view, lately so 

 well figured and described by Spencer 1 for Stenaster ob- 

 tusus. The abactinal arm-view of Ste.naster salteri 

 not having been figured as yet, we give here that side in plate XI, 

 figures 1 and 2. It is essentially alike as in S . obtusus, the 

 Bfitish Ordovician representative of our species. 



The new characters which are recognizable in our two specimens 

 are the presence of a dorsal integument and an interradial disk. 

 Schuchert had already observed interbrachial areas in a specimen 

 of S. salteri regarding which he states (op. cit., p. 166): 



In the University of Toronto there is a specimen that .in every 

 way, except one, has the characters of Stenaster salteri. 

 It was found associated with many other individuals at Kirkfield. 

 It differs from its associates in having what appears to be a distinct 

 disk, rather large, with concave sides, filling in the spaces between 

 the rays. One looks in vain, however, for plates or spines, as the 

 interbrachial areas are nothing more than an amorphous mass of 

 calcium carbonate. These areas are very distinct and stand out 



1 W. K. Spencer. A Monograph of the British Palaeozoic Asterozoa. Pt 1. 

 Palaeontographical Society 1913(1914), pi. 1, fig. 7. 



