246 Prof. P. M. Duncan on the Saleniclte. 



of different ages, there is a marked distinction between 

 their apical systems which has nothing to do with age and 

 which transcends any variation. The new form is a true 

 Salenia 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, o{ Peltastes) ^ and it presents in the figure 

 altogether abnormal characters as one of the Salenid^e*. The 

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

 has all the generic characters of the true jSalenice, and thus is 

 more closely allied to the new form than to Salenia varispina. 

 The questions arise, then, Are the new form and Salenia vari- 

 spina varieties of a type, or are there three recent species of 

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

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

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

 great a difterence between his and the other forms of recent 

 Salenidge as there is between some of the fossil species of 

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

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

 assume the position usually supposed to be characteristic of 

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

 generic title of ;S'. varisjnna ; 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 Salenida^ 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 : — 



SALENIDJi. 



Peltastes van'spt'ua, Agass. sp. 1 



Salenia Goesiana, LoAen. > Recent. 



Sale?jia profundi, robis. ) 



Salenia tertiaria. Tate t- Australian Cainozoic. 



Salenia Pellati, Cotteau J. Eiarritz Nv.mmulitic. 



The specific characters of the new species will be given 



* " The abactiral system has the structure cf that of Salenia ; but the 

 position of the anal system is that of Ifi/posal<nia." (A. Agassiz, 'Eev, 

 Echini,' \b72, p. 261. Ccmpaie his plate iii. f. 8-14 with this state- 

 ment.) 



t^Prof. E. Tate, F.G.S., Quait. Joum. Geol. Soc. vol. xxxiii. p. 258, 

 18/ 7. 



:1 M. G. Cotteau, Revue et Mag. de Zool., Mai 1860, p. 212 (Raiis). 



