176 PROF. p. M. dutstcak's eettston op the 



those of the other; usually the postero-lateral radial pJates are 

 in contact ; or complementary plates may separate the postero- 

 lateral basals and radials. 



Ambulacra unequal, flush or slightly raised, open at the end 

 of the subpetaloid parts ; pairs of pores in simple series, more 

 or less unequal in shape and size, the outer elongate ; below the 

 subpetaloid part the pores in small oblique pairs, conjugate or not. 



Peristome excentric in front, deeply seated, pentagonal, elon- 

 gate or rarely circular, elliptical, transverse or oblique ; without 

 bourrelets, and with very rudimentary or absent phyllodes, and 

 only slight doubling of pores. Periproct usually elongate longi- 

 tudinally, may be transverse, placed at the upper part of the 

 posterior groove, which extends with variable lengths towards 

 the apex ; periproctal membrane with large plates near the edge. 

 Tuberculation small, larger actinally. 



Fossil. Oolite : England, Europe, A.sia. Cretaceous : England, 

 Europe, N. Africa, Asia. Eocene : Europe. Tertiary (late) : 

 Australia, N. Zealand, Java. 



Subgenus Dochmostoma.. 



Syn. Trematopygus, (genus) d'Orb. 



Peristome oblique. 



Fossil. Cretaceous : Europe, N, America. 



Subgenus Oligopodia. 



Ambulaeral pores single below the petaloid part. 

 Becent. New Zealand, Madagascar, East Indian Islands. 



Cotteau has probably seen and examined more species of EcM- 

 noirissus thaa any other palseoutologist, and as far back as 1871 

 he gave an amended diagnosis of the genus in Pal. Pran9., Terr. 

 Jura, ix. p. 233. He noticed the variability of the position of the 

 madreporite and of the periproct. Later, in 1884, the same 

 careful observer (Bull. Soc. Zool. de Prance, p. 336) stated that, 

 after a study of twenty-six species, he found that the madreporite 

 in general touches the postero-lateral basal plates, and that 

 sometimes it separates these plates, aud it may even separate 

 the postero-lateral radial plates; even complementary plates 

 may separate the basal plates and the radials, these structures 

 not being seen in all individuals of the same species. The peri- 

 proct varies in its position from touching the apical system to 



