ECHINOLAMPAS DEPRESSA. 47 
another containing those in which there is a marked difference in the length 
of the poriferous zones of the ambulacral petals, and a third, which Bell has 
called Palasolampas, characterized by the straight apetaloid ambulacral zones. 
The differences in the petaloid ambulacra are accompanied by other struc- 
tural features, such as the position and outline of the anal system, and the 
character of the phyllodes and bourrelets, forming combinations of characters 
which a revision of the genus may show justify this subgeneric division. 
But as has been already pointed out by Cotteau and De Loriol, such a sub- 
division is impracticable if we take into account the numerous fossil species 
of Echinolampas. The subdivision of the genus to which Echinolampas depressa 
belongs is also marked by the absence of intercalated plates in the formation 
of the phyllodes (PI. XVI. Fig. 4), and by the prominent apical button 
formed (PI. XVI. Fig. 5) by the madreporic body, much as in Conoclypus. 
The characteristic uniform tuberculation of the test of ^. depressa is seen in 
the different figures of Plate XVI. On the actinal surface there is a narrow 
band in the median ambulacral areas towards the actinostome. The abac- 
tinal surface of the test is covered by slender radioles ; the radioles of 
the abactinal region are slightly shorter, increasing in length towards the 
ambitus, and becoming somewhat longer on the actinal side. The mili- 
ary spines are about a third of the length of the primary spines. When 
alive, the spines are of a greenish yellow color ; the test, of a dirty yellow 
color. It is interesting to note that, of the many fossil species of Echino- 
lampas described by Cotteau* from the West Indies, only two, E. Casiroi 
and E. AnguiUce, show any marked difference in the length of the poriferous 
zones of the petaloid ambulacra. 
On PI. XXIV. is figured the youngest stnge of Echinolampas I have seen. 
It measures 5 mm. in longitudinal diameter. The apical system is already 
eccentric ; but in this stage the ambulacra are simple, showing no trace at 
the apex of rudimentary petals. The actinal system is circular, and the 
anal system is still on the posterior face of the test ; the bourrelets are in 
the simplest form possible, a slight swelling of the ambulacral area at the 
actinostome, but the tuberculation is not diffei^ent from that of the other 
part of the ambulacra. 
* Cotteaii, Ann. Soc. Geol. de Belgique, 1881, IX., PI. II. Echinides Tertiaires des Isles St. Barthele- 
my et AiiguiUa, K. Vet. Akad. Handl., B. XIII., No. 6, PI. IV., 1875. 
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