246 Prof. P. M. Duncan on the Salenidi^. 



of difterent ages, there is a marked distinction between 

 their apical systems wliich has notliing to do with age and 

 "which transcends any variation. The new form is a true 

 Salcnia in respect of the position of the extra or subanal plate 

 and of the anal opening ; but the form described and figured 

 by A. Agassiz has, as he has noticed, the characters of Hypo- 

 salenia (^that is to say, oi Felfastes), and it presents in the figure 

 altogether abnormal characters as one of the Salenidaj*. The 

 Salenm Goesiana, Loven, small as the only specimen is, still 

 has all the generic characters of the true i>ah'nice, and thus is 

 more closely allied to the new form than to Salenia varispx'na. 

 The questions arise, then. Are the new form and Saleni'a i-ari- 

 spi'na varieties of a type, or are there three recent species of 

 kSalenidai ? In endeavouring to reply, the value of the generic 

 attribute of Feltasfes interferes to a certain extent, and it must 

 be admitted that the figures given by A. Agassiz indicate as 

 great a ditlerence between his and the other forms of recent 

 ISalenida? as there is between some of the fossil species of 

 Salenia and of Pclfastes. If it can be admitted that it is 

 within the variability of a species of Salenia for the amis to 

 assnme tlie position usually supposed to be characteristic of 

 the genus Pelfastes, there is no necessity for the alteration in 

 generic title of S. varisjjina ; but as yet there is no right to 

 assume it. Under the circumstances, indisposed as we ought 

 to be to alter the generic position of a previously described 

 species and to found a new species on one specimen alone, it 

 appears nevertheless advisable to place the interesting form 

 described by A. Agassiz in the genus Peltastes. 



The recent Salenidfe may be therefore arranged as follows ; 

 and as this communication will deal with the Tertiary forms 

 also, it is as well to introduce their names : — 



Salexid.e. 



Peltastes varisphw, Agass. sp. 1 



Salem'a G'oesiana, Loven. > Recent. 



Solatia jwofiindi, robis. ) 



Salent'a tirtian'a. Tate t. Australian Cainozoic. 



Salema Fellati, Cotteau J. Biarritz Kummulitic. 



The specific characters of the new species will be given 



* '' Tlie abactiral system has the stnictnre cf tLat cf Sahnia ; but the 

 position of the anal system is tLat of Hiiposclinia.'" (A. Agassiz, ' Eev. 

 Echini,' 1^7:?, p. 261. Ccmpare his plate iii. f. 8-14 with this state- 

 ment.) 



t Prof. E. Tate, F.G.S., Quait. Joura. Geol. Soc. voh xxxiii. p. 258, 

 1877. 



:| M. G. Cotteau, Eevue et Mag. de Zool., Mai 1860, p. 212 (Paiis). 



