530 Prof. J. F. Blalie—On Solaster Miirchisoni. 



examination is that they are undoubtedly of the same species, and that 

 therefore they both belong to the genus Solaster. 



The new example, however, is so much better preserved, and 

 renders the possible description so much fuller and more accurate, 

 that it is worthy of as much consideration as if it had been a new 

 species. 1 shall therefore describe it fully. 



Solaster Mukchisoni, Williamson (sp.). 

 Syn. 1836. Luidia Murchisoni, Williamson, Mag. Nat. Hist. vol. ix. p. 425. 

 ,, 1865. Solaster polynemia, Simpson, Fossils of the Yorkshire Lias, p. 135. 

 ,, 1863. Luidia Murchisoni,'Wx\g\A, Palseontographical Soc. p. Ill, pi. v. fig. 2. 



Diagnosis. — Diameter 4-6 in. Central aperture \ diameter. Eays 

 20-22. Angle-plates long, triangular. Ambulacral area with a pair 

 of ossicles, anvil- shaped. Pores large. Interambulacral area half 

 clothed, ossicles 5 on ventral surface, each with a spine, terminal one 

 with two. Dorsal surface with branching ossicles loosely netted. 



Description. — The new specimen is about 4 in. in diameter. It 

 has been buried in the stone with its ventral surface downwards, 

 by which means an external cast has been produced of the ventral 

 surface of its arms. Upon this has been pressed down the dorsal 

 surface which covers over and hides the central opening, and shows 

 sharply marked triangular, or bent impressions irregularly scattered, 

 which are interpreted as the casts of a loose network of dorsal 

 ossicles. The arms are 22 in number (see Fig. 1). Some are broken, 

 but most are complete, and come to a rather blunt termination. 

 Along the centre of each (see Fig. 2) is seen a raised band, cor- 

 responding to a depression in the animal. This band is threefold, 

 the centre line is the interval between the ambulacral ossicles, which 

 are like anvils placed back to back, as seen in the depressions of the 

 cast. The pores are large and form the two outer bands, occupying 

 the concavity of the ambulacral ossicles. Each of these ossicles is 

 continued outwards and also somewhat radially by a subtriangular 

 ossicle — and then by four others — all of the interambulacral series. 

 Each of these four had a spine in its centre, and the outermost an 

 additional larger one at the end. These latter clothe the sides of 

 the rays with a layer of spines. It is possible there were smaller 

 spines also on the softer part which intervened between each of 

 these rows of interambulacral ossicles and the next. These rows 

 form cross lines in the cast, with a gentle concavity in the radial 

 direction, and each ray has nearly 50. In one spot a fragment of 

 a ray has been reversed and its dorsal surface is seen. This shows 

 the insertions of the spines at the sides ; but the remainder is so 

 smooth that the paxillee must have been very small. This is all that 

 can be learnt from this specimen, which is beautifully preserved in 

 a fine micaceous, earthy sandstone, well suited to retain impressions. 



The original specimen, now in the Scarborough Museum, under 

 the charge of Mr. Phillips, who gave every facility for its examina- 

 tion, is in a shaly matrix, which, in spite of preserving materials, 

 has cracked, and is very liable to shale off entirely. It shows 

 ■20 arms and the central apertui-e is well-preserved, being about ^ of 

 the whole diameter. The inner ends of the rays open out in the 



