166 BULLETIN 88, UNITED STATES NATIONAL MUSEUM. 



Their length is about twice their breadth, and they are so disposed 

 that the greater dimension is transverse or at right angles to the 

 groove; the extremities which lie next to the grooves are angular, 

 and some of them appear to have the contiguous pores partly exca- 

 vated in them. The oral plates [adambulacrals] are acutely triangu- 

 lar, the sharpest angle being toward the mouth [and form the inter- 

 brachial areas]. The plates are smooth [the adambulacrals are all 

 distinctly granular]. The ambulacral pores are very large, and the 

 ossicles are much contracted in the middle and greatly expanded 

 along the median line of the bottom of the groove." These plates 

 are directly opposite one another and the adambulacrals, and in 

 number equal those of the latter. 



The type-specimen figured by Billings measures: R = 14 mm., 

 r = 3.5 mm., R = 4r. Width of a ray at base about 4 mm., at about 

 mid-length 5 mm. The largest specimen: R = 20 mm., r = 4.5 mm. 

 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 inter- 

 brachial areas are nothing more than an amorphous mass of cal- 

 cium carbonate. These areas are very distinct and stand out prom- 

 inently, but because they do not reveal any plated or spiniferous struc- 

 ture the writer regards them as false characters, produced during the 

 permineralization of the specimen. This conclusion is further sup- 

 ported by the fact that otherwise the characters are those of S. 

 salteri. 



Formation and locality. — Three specimens (the type, ISTo. 1398, and 

 two fragments) are from the Trenton limestone at Belleville, Ontario, 

 and are now in the IMuseum of the Canadian Survey. Another 

 specimen in that museum is on the same slab with Petraster rigidus 

 and has been labeled Palxaster matutina. In Mr. Ulrich's collection 

 there are four isolated rays of this species obtained by him from the 

 Black River limestone at Curdsville, Kentucky. A further specimen 

 preserving two rays, from Government House Bay, Ottawa, was found 

 by Mr. Walter R. Billings. In the Museum of Comparative Zoology 

 there is still another individual which appears to be of this species; 

 it was found by Mr. J. B. Perry at Panton, Vermont. Finally, an 

 abundance of material was obtained in the Black River limestones 

 at Kirkfield, Ontario; there are more than twenty specimens from 

 this locality in the Walker collection of the University of Toronto, 

 gathered by Mr. Townshend. 

 Cat. No. 60628, U.S.N.M. 



