86 



Dr. Tb. Mortensen on some EchinotJiurids 



wanting in this species is in accordance therewith. A more 

 advanced stage is shown by A. tessellatiim, whereas the 

 exquisite form of tetradactylous pedicellariae found in A.fenes- 

 tratum and coriaceum assigns to these species the highest 

 place in this series of species. The " tetradactylous " pedi- 

 cellariae of HapaJosoma sliow tliis genus to be derived from a 

 form with three-valved "tetradactylous" pedicellariee, like 

 A. Owstcni, The relations of these forms may be graphi- 

 cally shown thus : — 



A . fenestratum. 



A. coriaceum. 



HapaJosoma pellucidum. 



A. Owsteni. 



De Meijere ('Siboga' Echinoidea, p. 36) finds in two of 

 Lis specimens of A. tessellatum the small form of tridentate 

 pedicellavije identical with those found by me (' Ingolf ' 

 Echinoidea, p. 52, pi. xiv. fig. 20) in the specimen from 

 'Challenger' St. 219 referred by Agassiz to Calveria 

 Q' Asthenosoma") gracilis', in the other specimens they are 

 like those of the type specimen (' Ingolf ' Ech. pi. xiv. 

 fig. 15) : " Es fragt sich da ob dasselbe nicht rait deni 

 erwahnten Exemplar der St. 219 identisch ware"; he 

 suggests that this specimen is only a badly preserved specimen 

 of A. tesseJhitum. Through the kindness of Professor F. 

 Jeffrey Bell the specimen in question was sent to Copen- 

 hagen, so that I have been able to examine it closely, and 

 can give figures of it (PI. IV. figs. 3, 4). It is a young 

 specimen (30 mm. diameter), without genital openings, not 

 very badly preserved, the structure of the test being even 

 excellently seen ; but of pedicellarife no more can be found 

 than what I have already made known in my ^Ingoif^ work; 

 the spines are all broken. The actinal side is like the inner 

 part of the actinal side of the type specimen of A. tes^eUatumj 

 as figured in * Challenger ' Ech. (pi. xix. a. fig. 1), with a 

 primary tubercle at the outer end of each interambulacral 



