72 AGASSIZIA EXCENTEICA. 



The position of the ambulacra! and interambulacral areas was indicated by 

 the presence of rows, more or less irregular, of rudimentary, primary, and 

 secondary tubercles ; those of the actinal plastron and of the interambulacral 

 areas being generally more closely defined than those of the ambulacral 

 areas. In this stage the actinostome is pentagonal, with rounded corners, 

 the posterior lip being but slightly indicated. 



In a specimen measuring 6 mm. in longitudinal diameter, the posterior 

 lip is quite pronounced, and the actinostome has become transversely ellip- 

 tical, but the number of buccal tentacles has as yet not increased. The 

 granulation covering the test of the youngest stage examined (3 mm. long) 

 is arranged in short parallel lines forming irregular lozenges, perhaps like 

 those figured by Loven in the actinal system of several other Echini ; * but 

 the boundaries of these figures, if they have any regularity, could not be 

 traced. This stage of the test of Agassizia, covered as it is by a fine gran- 

 ulation such as we find characteristic of the granulation of the fascioles in 

 some of the Spatangoid genera, naturally suggests the idea that the fascioles 

 are merely bands formed by the remnants of the embryonic granulation of 

 the test on which tubercles proper have not yet developed. This rudimen- 

 tary granulation, arranged in more or less regular lozenge-shaped figures, is 

 a very general structural feature of the coronal plates of many Echini, in 

 which we can trace it readily in the younger stages. See especially Salenia 

 and young Echinidae and Cidaridae, as well as other Spatangoids. It is also 

 found in the structure of the plates of the calyx of many Crinoids, and 

 of some plates among the Starfishes, and we are justified in regarding this 

 granulation as the typical structural ornamentation of Echinoderms, which 

 has become specialized in recent times to form among the Spatangoids the 

 so-called fascioles. This would explain the presence of detached bands of 

 fascioles parallel to the principal ones, such as we find in Maretia, Ilomo- 

 lampas, Paleopneustes, Macropneustes, and Brissopsis. 



If this view of the nature of fascioles is correct, we should be justified 

 in considering the papillae of the Cidaridae arranged regularly round the 

 primary spines of the interambulacral areas, as well us the ambulacra! pa- 

 pillae, as modified fascioles not occupying special limited areas. The same 

 would lie true of the papillae of the Saleniae. A similar explanation would 

 hold good \'<>\- the down-like spines covering the greater pari of the tesl of 

 Aspidodiadema, and the long hair-like spines of Echinothrix, Centrostepha- 



* Lovrn. Btudes sur les fichinoidet i, Pis. XIX.. XXI. 



