80 



of the disc, rounded at the end ; ossicules all convex, rounded. Mar- 

 ginai ossicules \^, large, round, those near the end of the arms largest 

 and most convex. 



Inhab. W. Australia. 



This species differs from P. pidchellus va the marginai ossicules 

 being more equal, and in the arms being much longer and more 

 slender. The ossicules of the dorsal disc are uneąual in size and 

 rather irregularly formed ; those near the margin on the middle of the 

 sides are oblong and narrow, those of the orai surface are more re- 

 gular and not so convex, those near the angles of the mouth being 

 the largest and subtriangular. 



I have named this beautiful species in memory (I regret to say) of 

 M. W. Von Diiben, who has lately published a very admirable paper 

 on the northern species of this family. 



TosiA, Gray. 



The granules between the ossicules are deficient in the dead and 

 washed specimens. It has been thought that the fossil species found 

 in the chalk belonged to this genus, but the surface of the ossicules 

 of most of the specimens I have seen show, from the scars with w'hich 

 their surface is covered, that they were covered ■with gi-anules, there- 

 fore they rather belong to the restricted genus Astrogonium'., 



In some species of this genus the ossicules of the orai disc are more 

 or less entirely covered with crowded, flat-topped granules. 



TOSIA GRANDIS. 



Dorsal ossicules very uneąual, flat-topped. Marginai ossicules 

 i|. or i^ on each side, rather 'convex ; the ossicules of the orai sur- 

 face are furnished \vith tvvo or three rows of crowded granules, and 

 those near the ambulacra are most covered. 



Inhab. Western Australia. 



Link, under the name of P. regularis, t. 13. f. 22, 23, copied 

 (E. M. t. 96. and Seba, iii. t. 8. f. 4) a species likę the above, but it 

 has only ten marginai platės. Miiller, who thought he examined 

 Link's specimen at Leipsic, describes it as havįng seven upper and 

 five under marginai platės. 



TOSIA ATJRATA. 



Golden yeIlow. Dorsal ossicules flat-topped, the five in the centre, 

 between the centrai lines of the arms, largest, and round ; the mar- 

 ginai ossicules \^, or if i rather convex and nearly equal (that nearest 

 tlie top not being longer tban the others) ; the ossicules of the orai 

 disc, cdl except a few in the middle of each area, entirely covered 

 \vith flat-topped granules. 



Inhab. Australia. Brit. Mus., three spec. 



In others, the ossicules of the orai surface are only edged with a 

 single series of granules, likę those of the back. 



TOSIA TUBERCULARIS. 



Yellow, edges reddish. The dorsal ossicules convex, subtubercular. 



