ECHINOLAMPAS DEPRESSA IT 



another containing those in which there is a marked difference in the I 

 of the poriferous zones of the ambulacra! petals, and a third, which Bell lias 

 called Palaeolampas, characterized by the Btraighl apetaloid ambulacra] zones. 

 The differences in the petaloid ambulacra are accompanied bj 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 -runs may Bhow justify this subgeneric division. 

 Bui as has been already pointed oul 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. I i. and by the prominenl apical button 

 formed (PI. XVI. Fig. 5) by the madreporic body, much as in Conoclypus. 

 The characteristic uniform tuberculation of the tesl of E. depressa is seen in 

 the differenl figures of Plate XVI. On the actinal surface there is a narrow 

 band in the median ambulacra! areas towards the actinostome. The abac- 

 tinal surface of the tesl is covered by slender radioles; the radioles of 

 the abactinal region are slightly shorter, increasing in length toward- the 

 ambitus, .nu\ 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 spine- 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 [ndies, only two, /.'. Castroi 

 and A'. Anguillce, show any marked difference in the length of the poriferous 

 zones of the petaloid ambulacra. 



On PI. XXIV. is figured the youngesl stage of Echinolampas I have seen. 

 It measures 5 nun. in longitudinal diameter. The apical system is already 

 eccentric; but in this stage the ambulacra are simple, showing no trace at 

 the apes 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 simplesi form possible, a slighl swelling of the ambulacral area at the 

 actinostome, bul the tuberculation is not differenl from that of the other 

 part of the ambulacra. 



• Cotl I de Belgique, 1881, IX., PI. II. Echinict des Isli St Barthele- 



iny et Aii-mll.., K. Vet. Akad. II.in.ll , I'.. XIII., No. B, 11. IV., 1 



