Perignathic Girdle o/* Discoidea cyliudrica. 235 



Form of the Echinoconidse " (Bihang till Kongl. Svenska 

 Vet.-Akad. Handl. Bd. xiii. Afd. iv. no. 10), and explaining 

 why he had not noticed our paper upon the perignathic girdle 

 of Discoidea cylindrica, Lmk. Prof. Sven Loven wrote that 

 he could not reconcile our drawing (fig. 8, p. bQ) with the 

 results of his own observations upon several specimens, and 

 thai as he disliked animadversion he had thought it best to 

 publish his figures and to leave ours alone and uncriticized. 

 He also sent us his interesting paper, containing beautiful 

 illustrations. 



We thank our friend very cordially for his courtesy, but 

 we think that it is due to him that his discoveries should be 

 placed on record in a paper which will also do justice to 

 ourselves. 



We have nothing to retract or to add regarding the descrip- 

 tion given by us of the specimen in the British Museum. 

 Prof. Sven Lovdn's beautiful drawing shows, in addition to 

 what may be seen in the specimen we studied, distinct sutur- 

 ing of the interradial expansions of the girdle, some minute 

 plates at the ambulacra! edge of the interradial expansion, 

 but one pair of pores on either side of the ambulacral median 

 line, and that the outer pore of each pair is either along the line 

 of the ambulacro-interradial suture or beyond it and in the 

 edge of the interradial expansion. Tlie drawing by Prof. 

 Lovdn {op. cit. p. 9, fig. 1) gives the impression that the 

 parts of the interradial expansions next to the poriferous zones 

 are ambulacral and therefore relics of " processes " *. 



It is perfectly evident that Prof. Lov^n intended to convey 

 that these relics are tliose of " auricles " (ambulacral pro- 

 cesses in other terminology), and, indeed, in his description 

 of his fig. 2 he wrote '' Four auricles from the aboral side 

 and an ambulacral pair in the middle." 



It became necessary for us to examine other specimens, so 

 as to compare our results with those of Prof. Lovdn upon 



1. The position of the ambulacral pairs of pores. 



2. Comparison of the teaching afforded by the original 



specimen and by those of Loven. 



3. The sutures of the expansions in new specimens. 



Numerous specimens of Discoidea cylindrica were cut, and 

 without satisfactory results, the girdle being absent or ruined ; 

 but, thanks to Mr, Gregory, F.G.S., of the British Museum, 

 we have been able to study a very fairly preserved specimen. 



* The terminology will be found explained in Jouni. Linn. Soc, Zool. 

 vol. xix. p. 179 (1886), "On the Perignathic Girdle of the Echinoidea." 



16* 



