330 Mr. J. W. Salter on some new Palceozoic Star-fishes. 



and margin, rather more than their own breadth apart, and set 

 on at the intersection of the reticular meshes which cover the 

 arms and the angles between the arms, but which are quite ab- 

 sent from the central portion of the disk. This central portion 

 above, which corresponds to the wide aperture of the mouth on 

 the under surface, is covered only by scattered, stellate, calcareous 

 spiculse of large size. A closer reticulation is found on the por- 

 tions between the arms, and the meshes become square in a 

 double row down the middle of the rays, and appear to corre- 

 spond nearly in position to the ambulacral bones of the under 

 surface. The latter are very slender and remote, even more so 

 than in P. vermiformiSf and form a broad ambulacrum, with 

 only a few reticular plates bordering it, which bear clavate spines 

 at intervals. The mouth-angles project a good deal inwards, 

 and are armed with short combs of spines. 

 Loc. Leintwardine. 



Protaster. 



The species on which Forbes founded this genus is inter- 

 mediate in size between the larger and smaller species here de- 

 scribed. But it presents the same essential characters, the parts 

 varying in proportion only : the plated disk, the arms reaching 

 nearly to the centre, and forming a pentagonal rosette, and the 

 double row of plates above and below. The largest form of the 

 genus is the 



1. P.Miltoni,u.s^. PI. IX. fig. 4. 



P. magnus, disco calcareo subrotundo, brachiis 3-4-uncialibus, latis ; 

 ossiculis incrassatis paribus, superne concavis, ad angulum internum 

 perforatis ambulacra* lato ; assulis oris rectis. 



The roundish disk of this conspicuous species is often more 

 than 1 inch wide, and covered with small ridged plates. The 

 arms are wide, composed of large ossicles, which become smaller 

 at their base of insertion in the disk above, leaving a wedge- 

 shaped space between, which, joined with those of the other 

 arms, forms a conspicuous pentagon above, equal in size to that 

 formed by the divergent ossicles of the mouth below. 



The arms themselves are made up of a double row of about forty 

 pairs of squarish concave plates above, placed exactly opposite, 

 not alternating as in other species (PI. IX. fig. 4, b). The sutures 

 between these are deep, and the inner angles marked with a 

 deep pit or pore, bounded by tubercles set cross-fashion. The 

 outer margin bears a tuft of spines, long and short. On the 



* The term may be conveniently applied to the pair of central plates 

 (subambulacrals), though they cover the true ambulacrum. 



