ROTULA RUMPHII. 543 



nearer the mouth than the edge ; it is transversely elliptical, larger than the 

 mouth, with slightly raised edges. The anal plates and spines of the two 

 surfaces were not preserved in any of the specimens I have had occasion to 

 examine. 



Liberia. 



Rotula Rumphii 



: Rotula Rumphii Klein, 1 734, Nat. Disp. Eeh. 



PI XHP.f. 6-7. 



This species is readily separated from its congener by the nature of the 

 digitation of the posterior edge. The outline of the test is circular, pointed 

 anteriorly. The greatest diameter is the longitudinal diameter, which is 

 slightly greater than the transverse. The opposite is the case in R. Augusti. 

 The edge of the test is thin, the central part higher ; the petals arching 

 regularly from their extremity to the apex. The vertex is anterior, but 

 closer to the apical system, which is almost central. The petals are small ; do 

 not extend so far towards the edge as in E. Augusti ; they are lanceolate, 

 pointed, with a tendency in the poriferous zones to approach towards the 

 extremity ; the poriferous zones are much narrower than the median inter- 

 poriferous areas. The interporiferous space is greatest in the odd anterior 

 petal, and the same in the lateral petals ; the posterior petals are shorter 

 than the anterior pair ; they, in turn, are shorter than the odd petal. In none 

 of the largest specimens examined do we find more than one or two of the 

 pores in the furrows connecting the outer and inner row of pores so markedly 

 developed in R. Augusti. The inner pore is the largest in this species. The 

 abactinal system is comparatively larger, less pointed ; but the position of 

 the ocular and genital pores is the same ; the apical system is more conical, 

 and still better isolated from the abactinal extremity of the petals than in 

 R. Augusti ; as in R. Augusti the petals are slightly swollen in the central 

 interporiferous part near the apex, while the median space, as well as the 

 whole of the petal, is flush with the surface of the test in R. Rumphii. 



The digitations of the posterior edge of the test vary greatly with age ; 

 they are entirely confined to the posterior interambulacral spaces ; the an- 

 terior pair of ambulacral notches and the anterior interambulacral lunules 

 of R. Augusti exist only as slight indentations. The notches extend only 

 somewhat more than one third the distance from the edge in the median odd 



