246 PBOI'. p. M. DUlfCAN's REVISION OV THE 



third plates form much of the surface on either side of the narrow 

 amphisternum, which, with the rest of the surface, is compara- 

 tively flat. Normal heteronomy of the interradium I. Great 

 nipping-in of the interradial plates below the periproct. 



Peristome excentric in front, crescent- shaped or subcircular, 

 with a well-developed posterior labrum ; the plates of the mem- 

 brane well-developed. The periproct posterior and pear-shaped, 

 in the truncated posterior surface, plated largely. 



A peripetalous fascicle, elliptical, undulating or not. A broad 

 subanal fasciole, surrounding a broad area, including six ambu- 

 lacral plates on either side and grooves radiating to their pores. 

 An incomplete anal fasciole, a vertical and small branch passing 

 from the subanal or from a horizontal fasciole placed immediately 

 above it, upwards on either side of the periproct, or in that 

 direction. 



Ornamentation abactinalJy either of very small close tubercles, 

 the largest on the flanks of the anterior groove, or there may be 

 , numerous, yet distant, large primary tubercles in the lateral in- 

 terradia, within the peripetalous fasciole. Beyond the fasciole 

 the small tubercles gradually increase in size to the ambulacra at 

 the peristome. Spines short, slender, curved, largest actinally 

 and with a milled ring. Spheridia numerous, in groups in all 

 the ambulacra. 



Fossil. Eocene : Europe, Asia. Tertiary : N. America, W. 

 Indies, Malta, Italy. 



Becent. West Indian Islands, Florida, Mexico, Eed Sea, 

 Pacific Islands, East Indian Islands, Australia, Mauritius, E. 

 Brazil, Sherboro Island, California, Mediterranean. Shallow 

 water to 156 fms. 



Genus Ehinobeissus, A. Agassiz, 1872, Bull. Mus. Comp. Zool. 

 p. Ill; Bevision, 1872-4, p. 590; 1881, Beport on 'Chal- 

 lenger ' Echini, p. 186 ; 1883, Beport on 'BlaJce' Echini, p. 67. 

 Test moderate in size, very thin, longer than broad and broader 

 than high. Outline from above ovoid, with a narrow posterior 

 end ; broadest on a line with the apical system, which is nearly 

 central or slightly in front. Vertex of the test posterior, and 

 the posterior surface is tall, truncated, and hollowed transversely. 

 Apical system small, with four bit sal plates with large genital 



