558 NUCLEOLITES EPIGONUS. 



doubt, prove these genera to be identical. In the subgenus represented by 

 epigonus, the actinostome is longitudinally elliptical, while it is transversely 

 elliptical in E. recens. In one subgenus the posterior extremity is verti- 

 cally truncated ; in the other the outline of the test is nearly uniformly 

 arched from the anterior to the posterior extremity; neither of these char- 

 acters seem to justify us in retaining permanently the genera Echinobrissus 

 and Nucleolites ; they are however retained, in order not to introduce new 

 complications from insufficient data, as neither of these species correspond 

 exactly to the genera Nucleolites and Echinobrissus, as recognized by Desor 

 and Cotteau, from the study of the fossil species, where considerable con- 

 fusion still exists. Wright does not admit the distinction made by Desor, 

 D'Orbigny, and Cotteau. and Forbes united Clypeus with Echinobrissus as a 

 subgenus, showing that the classification of this group is by no means sat- 

 isfactory as deduced from the examination of the fossil species alone. 



Nucleolites epigonus 



! Nucleolites epigonus Mart., 1865, Monatsb. Akad. Berlin, Marz, p. 143. 



PL XIX". f. 4-6. 



Test thin ; outline from above elliptical, rounded anteriorly, attaining its 

 greatest breadth opposite the posterior extremity of the posterior lateral 

 ambulacra ; truncated across the posterior ambulacra ; median interambu- 

 lacrum indented by a deep vertical anal groove. Lower side concave, sloping 

 rapidly from the swollen, bulging, lateral interambulacral vd^v to the large 

 actinostome. which is anterior, longitudinally elliptical. 



The outline in profile is regularly arched, falling towards the anterior ex- 

 tremity from the nearly vertically truncated posterior edge ; the vertex is 

 placed immediately anterior to the deep anal groove ; the anal system is 

 longitudinally elliptical, placed at the bottom of the groove ; the edges of the 

 groove are sharp near the upper end, but gradually become rounded towards 

 the actinal surface ; apical system anterior; madreporic body flush with the 

 test; four large genital openings. The petals are of nearly uniform width, 

 and equally developed ; the posterior pair extending somewhat beyond half 

 the distance between the apical system and the edge ; they are slightly 

 larger than the others. The other petals extend to within a short distance 

 from the edge ; the median interporiferous zone is broadest in the odd an- 

 terior petal, and narrowest in the posterior pair; from the extremity of the 



