238 On a Species o/Echinoconus. 



either side of the median line are homologous with the "ridges" 

 and the other plates with the " processes." 



According to the inferences which arise after studying the 

 British-Museum specimens, the median plate is one plate of 

 a " ridge" and those on either side of it are other plates of 

 the same structure. There is no arabulacral process. 



If it is admitted, as it well may be, that the specimens in 

 the British Museum have had the plates on either side of the 

 median suture so fused that the union is no longer visible, 

 the clear definition of the ambulacral areas indicates that no 

 portion of an ambulacrum exists on the Hanks of the interradial 

 expansions. From the evidence before us, and after studying 

 Prof. Lov^n's Hgures, we hold that ambulacral processes or 

 their homologues are absent and that the expansions are 

 analogous to, and to a certain extent homologous with, the 

 " ridges " of Cidaridffi. 



It must be remembered, however, that in Di'adeina setosum 

 the " ridges " of the perignathic girdle have a median sutural 

 line separating two plates, on either side of which is a plate 

 clearly belonging to the interradium. The gradual evolution 

 of this arrangement can be appreciated by comparing figures 

 41, 42, 43, and 49 in Journ. Linn. Soc, Zool. vol. xix. 

 pi. xxxi. 



Fmally we regret to differ from our friend respecting the 

 presence of jaws and teeth in the genus Discoidea. We 

 cannot find any probable or demonstrative evidence in favour 

 of their existence. 



Echiiioconus {= Galerites). 



Prof. Lovdn believes that a structure similar to that of the 

 perignathic girdle of Discoidea cylindrica " maintains in 

 Oalerites alhognlerus^'' that is to say in Echinoconus. He 

 also credits this well-known species with jaws and teeth. 



In the ' Geological Magazine,' 1884, dec. iii. vol. i. no. 1, 

 p. 10, one of us enlarged upon the nature of the peristomial 

 structure of Galerites alhogalerus=- Echinoconus conicus^ and 

 proved that the so-called teeth described by E. Forbes and 

 Wright are buccal plates (p. 18) ; no jaws or teeth have been 

 found. 



It was explained that no auricles have been seen in any 

 specimen preserved in the British Museum, and that whilst 

 the ambulacra are without processes there is thickening of the 

 interradia close to the peristome. 



The whole matter has been reconsidered and with the same 

 results. The five ambulacra end distinctly at the peristomial 



