2 



BEITISH FOSSILS, 



of the family of Urasteriadije, a group distinguished by the presence 

 of four rows of suckers in each ambulacral avenue, but belongs to 

 one of the genera in which there are but two rows of ambulacral 

 feet. The peculiar arrangement of the ossicles of the disk, which 

 are perfectly preserved in the specimen, the forms of the ambulacral 

 ossicula, the single series of interambulacral bones, the arrangement 

 and shape of the spines on the border of the avenues, and of the 

 ossicula at the basal angles of the arms, all indicate its probable 

 position in the genus Solaster. 



The diameter of the individual figured, measured from r?vy point 

 to ray point, is somewhat more than 5 inches, the disk is 1 inch 

 and -pV across, and a ray is 2 inches long, and -pV of an inch 

 broad at its widest part. The average breadth of an ambulacrum 

 is -J--- of an inch. There are thirty-three rays, in all of which the 

 ambulacral portions as well as the borders are beautifully preserved. 

 The extremities of some of the rays are partially turned over, but the 

 portion of the dorsal surface thus exposed is obscured by crushed 

 spines. The inner surface of the dorsal integument of the disk 

 occupies the centre, all the ventral portions of that region having 

 disappeared. The framework of the dorsal disk is for the most 

 part excellently preserved. The skeleton in this region is composed 

 of a number of rather stout and vertically compressed oblong 

 ossicles overlapping each other slightly, arranged in a loose and 

 somewhat irregularly reticular pattern. The connecting ossicula 

 are most perfectly seen, the spiniferous ones being partially con- 

 cealed by their supporters. Towards one side of the disk is a 

 rounded impressed space with traces of a wrinkled surface. This 

 I take to be the position and remains of the madreporiforra 

 tubercle. 



The position of the vent cannot be clearly traced ; a circumstance 

 by no means surprising, considering the difficulty there is in ob- 

 serving the place of this orifice in the living star-fishes. 



The arms are very narrow, and of a linear shape ; their sides 

 being parallel throughout the greater portion of their length. At 

 the point of junction of the base of each arm with that of the next, 

 is a pair of erect semi-circular, compressed, slightly sinuous, sharp- 

 edged bones (the angie-ossicula). Their inner edges, i. e. those 

 directed towards the mouth, approximate ; their outer edges are 

 divergent. Their upper edges spread outwards, but much less so 

 than in the corresponding bones in the recent Solaster jiaioposus, 

 and they are much more compressed and elevated. Along their 

 outer margin are rows of slender spines. 



