36 SVEN LOVEN, ECHINOLOGICA. 



sally, and Avliile tlie wliole of thein is slowly pressing dowii- 

 ward in the direction of tlie stonia, the new ambulacral plates 

 are transformed, if not in all tlie Ectobrancliiates, at least in 

 their greatest majority, from being primitively simple and en- 

 tire into secondary compound plates, consisting of entire and 

 demi-plates in regular succession, and finally coalesce near the 

 peristome' in suck a manner tliat the adoral termination of 

 the column instead of being, as in the (Jidaridte and Eehino- 

 thnrida?, in a state of continual pliancy constantly renewed, 

 becomes a solid barrier against the flexible buccal membrane. 

 The inner surface of the peristome thiis Consolidated is in the 

 Ectobranchiates the site of the auricles. 



It was Blainville- who in 1825 first drew attention to 

 these projections as they exist in genus Echinus of Lamarck. 

 The appellation auriculse, evidently suggested by the form of 

 their arched pairs of branches often recalling that of the ears 

 of a vessel, has l)een universally adopted and possesses every 

 claim to be kept up. 



The early appearance of these parts, in the astomous stage, 

 has been deseribed above pag. 14, IG. On every ambulacrum the 

 two branches of an auricle are commencing to form. Fl. IV, 

 fig. 26, each of them at lirst a slight deposit of calcified re- 

 ticular tissue, a low projection differing in aspect from that 

 of the plate from which it rises, extending a little beyond the 

 near suture, upon the solitary interradial adjoining. At a 

 låter stage of the astomous period, they are seen to rise, to 

 begin to diverge and to arch över the ambulacrum, and their 

 basilar expansions are marked from the plate b}' a distinct 

 suture, Fl. T, fig. SO, 31. 



When the skeleton of an adult specimen of an Ectobran- 

 chiate is broken to pieces, the auricles are found invariably 

 to adhere to the ambulacra and to separate from the inter- 

 radia. The nature of their connection with the ambulacra is 

 revealed by that same suture,-^ more or less distinct, but with 

 some care observable in any species. The woodeuts annexed 

 represent its position on the peristome of two types of this 

 division which in other respects are widely different, the Dia- 

 dema saxatile L., and the Tripneustes esculentus Leske, of the 



' Etudes s. 1. Echinoidées, p. 20, Pl. XVII. 



* Dictionnaire des Sciences naturelles, XXXVII, p. 02, 73. 



' Etudes, p. 19, 28. 



