Zoological Society. 201 



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

 ginal ossicules \%, large, round, those near the end of the arms largest 

 and most convex. 



Inhab. W. Australia. 



This species differs from P. pulchellus in the marginal ossicules 

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

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

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

 sides are oblong and narrow, those of the oral 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 Duben, 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 which 

 their surface is covered, that they were covered with granules, there- 

 fore they rather belong to the restricted genus Astrogonium. 



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

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



Tosia grandis. f~ 5 I / 



Dorsal ossicules very unequal, flat- topped. Marginal ossicules 

 -^ or J-§- on each side, rather convex ; the ossicules of the oral sur- 

 face are furnished with two 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 like the above, but it 

 has only ten marginal plates. Miiller, who thought he examined 

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

 five under marginal plates. 



Tosia aurata. 



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

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

 ginal ossicules if, or if , rather convex and nearly equal (that nearest 

 the top not being longer than the others) ; the ossicules of the oral 

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

 with flat-topped granules. 



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



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

 single series of granules, like those of the back. 



Tosia tubercularis. fcT & 



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



