114 



ECHINOIDEA. II. 



On the actiual side the only more iinportant change occurs in the actinostome, the labruiii 

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

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

 enlargement of the piates. 



The Identification of these young specimens of Sc/i. fragilis is beyond doubt, both on account 

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

 that globiferous pedicellariæ 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 pedicellariæ — except < Heiiiiaster zona/uso^ which cannot be taken into con- 

 sideration here, as it has (as far as known) no latero-anal fasciole. Now, on the other hånd, 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 Dioviedæ seems to leave 

 no doubt that the latter is only the young of some Schizastcr-^^&cxzs from the Southern Atlantic', or 

 perhaps of a species of the genus Aba/iis, whose development is quite similar to that of Schizaster 

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

 to which Spatagodesma Dioviedæ 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 Be that as it may; the genus Spatagodesma must certainly be withdrawn as 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 faet that Spatagodesjna is really only the 

 young of some other well known genus, whether Sc/iizasfer or Abatiis — 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 piates 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 piates 

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

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

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

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

 and madreporite. 



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

 of the lateral fasciole. Professor Agassiz (iChall>.-Ech. p. 200) takes the faet, 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 development of the fascioles in 



" It was takeii off the Atlantic coast ot Patagonia, not off San Francisco, as stated in <iBronn» p. 1406. 

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

 Polar Expedition. 



