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 opinion- (p. loi); I confess my inability to under- 

 stand how a statement, showu to be erroneoiis, 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 vahie must be due to some error. So far 

 as I know 1 have never stated that tlie spicules are of no systematic vakie. On p. 45 I have said 

 that the spicules are almost ahvays rather large, irregular, fenestrated piates situated more or less 

 distincth' in 3 — 4 longitudinal series. In ^ J. varhuii, Grubei, Iictcractis and urens they are very slightl}' 

 developed, ouh' small, branched calcareous pieces, rarely with a hole . In the following lines I sa}' of 

 the sphæridiæ that the\- 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 Aræosoma and Calvcria is, I agree, not so very important, 

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

 argued by Dr. F. A. Bat her', it may, perhaps, be preferable to unite C. hystrix with the genus 

 Aræosovia : to the genws Asthenosoii/a it cannot be referred. The species ^-J. warm?« and Grubei I have 

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



Professor Agassiz claims to have figured au ophicephalous pedicellaria of iPhormosoma» lii- 

 culentiim. viz. on PI. XLIV. fig. 27 of the Challenger -Echinoidea. I may remark on this accouut that 

 he onh' mentious it in the explanation of the piates and under the name small short-headed, short-stemmed 

 pedicellaria ; further I have b\- no meaus 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 Doderleiu is right 

 in supijosing (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) pedicellariæ figured by me 

 OU PI. XIII. F~ig. 16 to be the same as that which he has figured in PL XLIV. 25 — 26 (« Challenger »- 

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

 valves, fiudiug that his figures «give a good represeutation of the single val ve*. 



That figures of Phormosonia plateiita are given in the Blake -Echiui and of Phorniosoma 

 biirsariinu in the Challenger -Echiui does not eliminate the faet, that Professor Agassiz in describing 

 the latter species only points out the differences from the distantly related . P/iormosomay> luculentum 

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

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

 reason for pointing out such differences appears also from the faet that Professor Doderleiu is now 

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



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

 suggesting any affinit}* between A. pelluciduvi and A. coriaceiiin and A. tesselafniii, because^ he has 

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



1 The Echiuoderui name Calveria hystrix. .\iin. Nat. Hist. 7. Ser. XVII. 1906. p. 249. 

 ^ The Italics are mine. 



