I 



Prof. P. M. Duncan on the Salenidje. 73 



sphajridia and true spines, Loven very justly observes that 

 there is a certain resemblance between the club-shaped radicles 

 of certain extinct Cidaridas and the sphjeridia of some other 

 groups. Considering the great diversity of the shape of the 

 spines in modem Salenice it is therefore very necessaiy to be 

 assured that the bodies just described are not young spines. 

 But their glassy appearance, their remarkable position at the 

 peristome end of the ambulacra alone, and their absence 

 from the interambulacra tend to prove that their resemblance 

 to the sphffiridia of Echini is on account of their being identical 

 structures. Very minute globular spines of Salenia are 

 striated and prickly on the top. 



Hitherto sphteridia have not been found in the Cidaridae, and 

 therefore their presence in the Salenia^ with the absence of a 

 series of imbricating buccal plates perforated by tentacles, 

 removes the genus and probably its congeners from their 

 present classificatory position. 



The pedicellariaj were noticed by A. Agassiz on the buccal 

 membrane ; but he did not find them on the test. Those in 

 the specimen before me are very regularly placed, and their 

 white, blunt, globose heads contrast very strongly with the 

 spinose ornamentation of the apical disk especially. Their 

 pedicle is moderately stout, often slightly bent, irregular in its 

 calibre, and never sufiiciently long on the apical disk to 

 permit of the head being raised much above the level of the 

 surrounding structures. The head somewhat resembles those 

 so common on the buccal membrane of Echinus norvegicus, 

 butit is more globose and the texture is denser. Some are found 

 on the small plates of the periproct. The pedicellariawith the 

 longest stalks are in more or less regular series in tlie ambulacra 

 between the rows of club-shaped spines. In the interambu- 

 lacra the scanty pedicellari^ have often long stalks and small 

 globose heads, becoming finer towards their top. 



EXPLANATION OF PLATE II. b. 



Fig. 1. Peristomial end of an ambulacmm, with sphseridia, spines, and 



tentacles, magnified. A pedicellaria is in the background. 

 Fig. 2. Sphseridium, magnified. 

 Fig. 3. The upper sphferidium, magnified. 

 Fig. 4. Part of the apical disk and pedicellariae, magnified. 

 Fig. 5. Pedicellaria from an ambulacnim, magnified. 

 Fig. 6. Pedicellaria from an iuterambulacrum, magnified. 



