Bd. VI: 4) THE ECHINOIDEA. 21 



are of considerable interest, especially the larger one, so that I feel justified in giv- 

 ing a short description of them, noticing the points of difference from canaliculata. 

 The measurements are as follows: 





Dia- 

 meter. 



Height. 



Apical 

 system. 



Anal 

 system. 



Peri- 

 stome. 



Width of 



Number 



of plates. 



Radioles. 



Ambulacra. 



Inter- 

 ambulacra. 



Ambulacra. 



Inter- 

 ambulacra. 





mm. 



mm. 



mm. 





mm. 





mm. 







mm. 



9 • • ■ 



42 



22 





II 



16 



4-5 



20 



42-43 



7-8 





d" . . . 



20 



II 



8.5 



5-5 



9 



2.4. 



IO 



30-31 



7-8 



26.5 



The younger specimen differs from an equally sized specimen from South Ame- 

 rica in the genital plates having a less prominent outer angle (PI. XIV Fig. 6). On 

 the peristome the interambulacral spaces are somewhat narrower within, the inter- 

 ambulacral plates thus scarcely reaching to the mouth-opening. Otherwise I do not 

 see any differences from the typical form. 



The larger specimen differs considerably more from the typical form. The 

 apical system is especially interesting (PI. XIV Pig. 10). The genital and ocular 

 plates have been greatly reduced, the former even partly split up into small irregular 

 plates, so that it can scarcely be said with certainty which of them represent the gen- 

 ital plates; only the madreporite has almost kept its original size. In accordance with 

 this reduction of the genital plates the anal system has greatly increased in size; on 

 account of the small size of the numerous anal plates it is somewhat movable, much 

 as in an Ecliinns. The whole apical system to some degree recalls that of the 

 Echinothurids (especially on account of the great reduction of the genital plates). 

 One is also reminded of the apical system of T>Stephanocidaris», the ->echinoid» cha- 

 racter of whose anal system is so persistently emphasized by Agassiz and Clark. 



The small upper interambulacral plates are closely covered with secondary tu- 

 bercles round the rather small areoles, whereas otherwise the upper plates are ge- 

 nerally more or less naked. This means, evidently, that this specimen has reached 

 its full size, and these upper plates are not increasing in size any more; likewise no 

 small, just beginning, plates are found at the outer sides of the genital plates, as are 

 elsewhere generally found. — The Fig. 7 PI. II of the »Challenger» Echinoidea pro- 

 bably represents a similar stage. — The upper radioles are also fully formed, though 

 considerably smaller than those at the ambitus. (Unfortunately I did not observe 

 the quite uppermost ones before denuding the apical part; evidently they have not 

 been longer than the secondary spines.) 



hese species — the more so, as the captain who brought the collection from Altata to Salmin had also 

 dredged on the coast of Patagonia in depths of 40 — 50 fathoms. After this I do not doubt that these 

 wo specimens are really from South America, not from Altata. 



