ECHINOIDEA. II. 



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

 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 actinal 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 pedicellarise 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 pedicellariae except <s.Hemiaster zonalus-*, which cannot be taken into con- 

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

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

 p. 198202. 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 Diomeda seems to leave 

 no doubt that the latter is only the young of some Sc/master-species from the Southern Atlantic 1 , or 

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

 fragilis? The pedicellariae might probably have given a definite answer to the question of the genus 

 to which Spatagodesma Diomeda 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 Be that as it may; the genus Spatagodesma must certainly be withdrawn as 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 Abatus -- 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 iuterambulacral plates in the apical system is something 



t 



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 ankylosed 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. fragilis 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 fascicle. Professor Agassiz (Chall.-Ech. p. 200) takes the fact, that the latero-anal 

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

 showing that the lateral fascicle is an extension of the anal fascicle*. The development of the fascicles in 



1 It was taken off the Atlantic coast of Patagonia, not off San Francisco, as stated in Bronn p. 1406. . 



2 The development of Abatus cavernosus will be treated in my Report on the Echinoidea of the Swedish South- 

 Polar Expedition. 



