20 ECHINOIDEA. II. 



fessor Agassiz remarks on this criticism: <I have stated that I thought this character of no great 

 systematic importance. Dr. Mortensen is of contrary opinions (p. 101); I confess my inability to under- 

 stand how a statement, shown to be erroneous, can be made good again by simply reiterating it, even 

 if this is done by so eminent an authority as Professor Agassiz. 



The statement that I use the spicules in the classification of the Echinothurids, after having 

 ^previously informed us that they are of no systematic value must be due to some error. So far 

 as I know I have never stated that the spicules are of no systematic value. On p. 45 I have said 

 that the spicules are almost always rather large, irregular, fenestrated plates situated more or less 

 distinctly in 3 4 longitudinal series. In A. varium, Grubei, heteractis and urens they are very slightly 

 developed, only small, branched calcareous pieces, rarely with a hole. In the following lines I say of 

 the sphseridiae that they show no differences so great that they can be of any systematic importance*. 

 Perhaps it is this remark which Professor Agassiz through some lapsus has referred to the spicules. 



The difference between the genera Arceosoma and Calveria is, I agree, not so very important, 

 and since the name Calveria cannot be used, as pointed out by Professor Agassiz and most carefully 

 argued by Dr. F. A. Bather 1 , it may, perhaps, be preferable to unite C. hystrix with the genus 

 Araosoma; to the genus Asthenosoma it cannot be referred. The species A. varium and Grubet I have 

 never referred to the genus Calveria, as stated by Agassiz (p. 84). 



Professor Agassiz claims to have figured an ophicephalous pedicellaria of =s Phormosoma-^ lu- 

 culentum, viz. on PI. XLJV. fig. 27 of the Challenger -Echinoidea. I may remark on this account that 

 he only mentions it in the explanation of the plates and under the name < small short-headed, short-stemmed 

 pedicellaria ; further I have by no means overlooked that figure, but mention it on p. 60 and p. 176, 

 suggesting that it may represent an ophicephalous pedicellaria, but stating that I have myself been 

 unable to find any similar form of pedicellaria in this species. I think Professor Doderlein is right 

 in supposing (Op. cit p. 121) that it does not really belong to this species. When Professor Agassiz 

 takes the peculiar modified form of tridentate (or perhaps ophicephalous) pedicellarise figured by me 

 on PI. XIII. Fig. 16 to be the same as that which he has figured in PL XLJV. 2526 (Challenger- 

 Echinoidea), he is quite right. I have stated that carefully on p. 60 and have given no figures of the 

 valves, finding that his figures give a good representation of the single valves. 



That figures of Phormosoma placenta are given in the Blake:>-Echini and of Phormosoma 

 bursarium in the Challenger > -Echini does not eliminate the fact, that Professor Agassiz in describing 

 the latter species only points out the differences from the distantly related 'tPhormosoma-A luculentum 

 but not the characters distinguishing it from the very closely related Ph. placenta. Neither are such 

 characters pointed out under Phormosoma placenta in the Blake-Echinoidea. That there was some 

 reason for pointing out such differences appears also from the fact that Professor Doderlein is now 

 inclined to regard Ph. biirsarium as only a synonym of Ph. placenta (Op. cit. p. 127). 



Further, Professor Agassiz says (p. 85): Dr. Mortensen thinks that I am wholly mistaken in 

 suggesting any affinity between A. pcllucidum and A. coriaceum and A. tesselatum, because* he has 

 suggested a new genus, Hoplosoma, for A. pellucidum, based entirely upon the structure of the pedi- 



1 The Echinoderm name Calveria hystrix-. Ann. Nat. Hist. 7. Ser. XVII. 1906. p. 249. 



2 The Italics are mine. 



