ECHINODISCUS LAEVIS. 533 



between the apex and edge of the test ; posterior extremity truncated, slightly 

 indented in the direction of the anal opening. Test much thicker than 

 in the other species of the genus. Vertex anterior ; apical system nearly 

 central. The posterior pair of petals are quite short; the anterior pair some- 

 what longer, but still considerably shorter than the odd petal. The outline 

 of young specimens is triangular, with rounded angles. 



The lunules are very long, narrow, sometimes narrower in the middle part, 

 forming an obtuse angle with the prolongation of the median axis of the 

 posterior petals. Seen from the actinal side, the ambulacral furrows are deep, 

 sharply cut, branching only once or twice quite near the edge ; they are very 

 prominent, as they are edged on both sides by minute tubercles, closely 

 packed, giving them the appearance of bare bands, greatly contrasting with 

 the coarse distant tuberculation of the remaining part of the actinal surface. 

 In the interambulacra the largest tubercles are placed along the bare bands 

 of the furrows, becoming smaller towards the median line and edge of test, 

 while in the three anterior ambulacral spaces the largest tubercles are in the 

 median space near the edge of the test, diminishing gradually in size towards 

 the actinostome. The mouth is small, almost central ; lobed. The anus is 

 small, circular, placed near the edge. The interior limestone network is very 

 compact, extending to the extremity of the petals, and leaving only a small 

 open space ; this is, however, completely smooth, showing no trace, except 

 a few ambulacral pits, of the delicate tracery covering the floor of the other 

 two species. The auricles are extremely small and low ; the teeth remark- 

 ably flat, even for this genus. The spines were not preserved in any of the 

 specimens I have seen. The color of dried specimens is dull olive-brown. 



Mozambique ; Red Sea ; Java. 



Echinodiscus laevis 



! Mellita laevis Klein, 1 734, Nat. Pisp. Ech. 



! Echinodiscus laevis A. Ag., 1872, Rev. Ech., Ft. I. p. 113. 



It is with considerable doubt that this species has been retained, although 

 I have examined considerable material representing from different localities 

 the E. auritus and E. laevis, and am not confident of having succeeded in 

 discriminating satisfactorily this species from its nearest ally, E. auritus. 



