SOLASTER. 



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Description. — This remarkable fossil Star-fish^ as it lies on the slab, with its under side 

 only exposed, has been likened to the head of a Crinoid, with outspread arms crushed flat, 

 but the structure of the rays at a glance discloses its true characters. It was referred by 

 Professor Forbes, who first described it, to the genus Solaster, as it has most affinities with 

 that group ; the concealment of the dorsal tegumentary skeleton, however, prevents us 

 from ascertaining with certainty whether it possessed paxillse similar to those in existing 

 species, and on which one of the main characters of the genus depends. In its general 

 outline, and in the proportionate size of the disc, and the number and linear form of the arms, 

 it resembles Heliaster helianthus, Linn., a many rayed species from the Pacific coasts of 

 South America. A closer examination, however, of the structure of the rays shows that it 

 belongs to a family in which the suckers are biserial, whereas all the TJr aster iadce have four 

 rows of holes for the passage of tubular feet. It differs from all the living Solasters in 

 having a proportionately smaller disc and a greater number of linear rays. 



The skeleton of the disc is well preserved, it consists of a number of stout, oblong, 

 rounded ossicles united together at their extremities, and forming a retiform structure, 

 having a number of stellate centres at the junction of the ossicula, which are crowded 

 together and overlap each other at these points ; (fig. 1 e) shows the reticular pattern of 

 the ossicles of the disc magnified. The connecting ossicula only are seen, the spiniferous 

 bones being concealed from view. 



The skeleton of the rays has been so well described by my lamented colleague Professor 

 Porbes, that I give the description in his own words. " The rays are very narrow and linear- 

 shaped, their sides being parallel throughout the greater part of their length. At the point 

 of junction of the base of each ray with that of the next, is a pair of erect, semi-circular, com- 

 pressed, slightly sinuous, sharp-edged bones, the angle-ossicula (fig. 4 d), their inner edges, 

 or 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 papjjosa. Linn. ; and they are much more compressed and elevated. Along their 

 outer margin are rows of slender spines which are admirably preserved in the specimen. 



Each avenue is composed of two series of ambulacral ossicles, about sixty in a row, 

 their inner edges being minutely crenulated and accurately meeting along the centro- 

 sutural line (fig. 1 U). These ossicles are shaped something like a dice box, each divided into 

 two more expanded portions and a central narrower part, (fig. 1 b). The inner portion 

 is flattened or slightly excavated, and somewhat rhomboidal, the outer elevated into a ridge. 

 The middle and more contracted portion is carinated obliquely, and on the inner (proximal) 

 side has a triangular groove. A similar groove occurs on the outer (distal) side, placed 

 nearer the middle than the former. The sides of the ossicles are widely excavated for the 

 purpose of forming the ambulacral perforation through which the soft suckers or ambu- 

 lacral feet passed. The inter-ambulacral ossicles are rather quadrate (fig. 1 c), and divided 

 diagonally, though somewhat irregularly, and lobe-like, into two portions, of which the 

 inner or inferior portion is elevated, and the outer depressed. These ossicles change 



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