72 AGASSIZIA EXCENTRICA. 
The position of tlie ambulacral and interambulacral areas was indicated by 
the presence of rows, more or less irreguhir, 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 Agassi zia, 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 jilates of many Echini, in 
which we can trace it readily in the younger stages. See especially Salenia 
and young Echinidte and Cidaridse, 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 j^arallel to the principal ones, such as we find in Maretia, Homo- 
lampas, Paleopneustes, Macropneustes, and Brissopsis. 
If this view of the nature of fascioles is correct, we sliould be justified 
in considering the papilla; of the Cidaridaj arranged regularly round the 
primary spines of the interambulacral areas, as well as the ambulacral pa- 
pillaj, as modified fascioles not occuj^ying special limited areas. The same 
would be true of the papillae of the Salenia). A similar explanation would 
hold good for the down-like spines covering the greater part of the test of 
Aspidodiadema, and the long hair-like spines of Echinothrix, Centrostepha- 
* Loveii, £tudcs sur Ics Kchinoidec\, Pl^. XIX., XXI. 
