jj. ECHINOIDEA. II. 



On the actiual side the only more important change occurs in the actinostome, the labrnm 

 widening at the anterior end until it has taken the place of the posterior half of the actinostome and at 

 last covers the mouth-opening. Other changes occurring on the actiual side are mainly due to simple 

 enlargement of the plates. 



The identification of these young specimens of Sch. fragilis is beyond doubt, both on account 

 of all intermediate stages being found, and on account of the pedicellarise ; it is especially to be noticed 

 that globiferous pedicellarite are developed already in the youngest specimens and of the same form 

 as in the grown specimens, but no other species of Echinoids of the Northern Atlantic, as far as I 

 know, has that type of pedicellarise — except 'iHemiastcr zonatiis-,-,^ which cannot be taken into con- 

 sideration here, as it has (as far as known) no latero-anal fasciole. Now, on the other hand, these 

 young specimens closely agree with the genus Spatagodesma A. Ag. (Panamic Deep-Sea Echini, 

 p. 198—202. PI. 106—7), founded by Professor Agassiz upon some young .specimens, about 5""" in 

 length. A comparison of the figures given here with those of Spatagodesma Dioincdcr seems to leave 

 no doubt that the latter is only the young of some Schizaster-s'^^Q\&s from the Southern Atlantic', or 

 perhaps of a species of the genus Abuhis, whose development is quite similar to that of Schizaster 

 fragilis}^ The pedicellarise might probably have given a definite answer to the question of the genus 

 to which Spatagodesma Diomcda- really belongs, but, unfortunately Professor Agassiz does not give 

 any information thereof. Be that as it may; the genus Spatagodesma must certainly be withdrawn as 

 a synonym of one of these genera. Professor Agassiz thinks Spatagodesma most nearly related to 

 Agassizia; this need not be further discussed, in view of the fact that Spatagodesma is really only the 

 young of some other well known genus, whether Schizaster or ^ibattis — but, of course, I will not 

 deny that the structure of the young may be of importance for judging of the relation of these genera. 



In the description of Spatagodesma Professor Agassiz points out that « there is a central apical 

 plate, composed of the four ankylosed genitals- ; but the left anterior ocular plate is, nevertheless, not in 

 direct contact with this ankylosed plate, it is separated therefrom by the intercalation of a row of lateral 

 interambulacral plates». This intercalation of interambulacral plates in the apical system is something 

 quite new in the Amphisternous Spatangoids, and probably Professor Agassiz has been lead to this 

 interpretation by his supposition of a close relation to Agassizia, in which genus all the genital plates 

 are really ankjdosed together. A comparison of the figure 2. PI. 106 (Pan. Deep-Sea Ech.) with the 

 figures given here of the apical system of the young Sch. Jragilis seems to me to leave no doubt that 

 the so-called intercalated interambulacral plates are really the two posterior genital plates, the large 

 central apical plate being not the ankylosed genital plates, but the single right anterior genital plate 

 and madreporite. 



The young stages of Sch. fragilis here described are especially important for the interpretation 

 of the lateral fa.sciole. Professor Agassiz ( Cliall .-Ech. p. 200I takes the fact, that the latero-anal 

 fasciole of Schizaster japonicus is sometimes interrupted on the sides of the test, as a proof « evidently 

 showing that the lateral fasciole is an extension of the anal fasciole:. The de\-clopment of the fasciolcs in 



■ It wa,s taken off the .\tlaiitic coast of Patagonia, not off San Francisco, as stated in iHr()nn» p. 1406. 

 ' The development of Aialtts cavernosus will be treated in my Report on the I^cUiiioidea of the Swedish .South- 

 Polar Expedition. 



