358 MEOMA VENTRICOSA. 



Spines of dried specimens of a yellowish-brown color, comparatively long, 

 especially in the anterior part of the test. Mouth large, longitudinal and 

 transverse diameter nearly as one to two ; posterior lip but little prominent. 



Genital openings round, close together ; posterior ones largest, slightly 

 more distant; madreporic body prominent. 



The anterior odd ambulacrum is flush with the test, and is marked by a dis- 

 tinct narrow band of closely crowded small tubercles extending from the 

 abactinal system to the margin of the test between the two rows of large 

 pores forming the odd ambulacrum. 



In smaller younger specimens we find the broad rounded posterior keel 

 less well defined, the anal system comparatively much larger, the subanal 

 plastron more elliptical, and the tubercles of the anterior extremity propor- 

 tionally much less prominent. Mouth comparatively more circular, ratio of 

 transverse to longitudinal diameter being two to one and a half. 



Littoral. 



(BRISSUS.) Meoma. 



Meoma Gray, 1851. Ann. Mag. N. H. 



Shell moderately stout, heart-shaped ; ambulacra (except odd one) sunk in 

 deep groove, the anterior and posterior pair nearly equal ; anterior ambula- 

 crum indistinct. Peripetaloua fasciole sinuous ; subanal fasciole more or less 

 imperfect, usually extending to the level of anal system as an open curve. 



Meoma ventricosa 



! Spatangus ventricosus Lamk. 1816. An. s. Vert. 



1 Meoma ventricosa LiJTK. 1864. Bid. til Kunds. ora Echin. 



PL XX. f. 8 ; PL XXII. f. 3, 4- 



Test moderately stout, broadly elliptical, slightly heart-shaped from above. 

 Actinal surface, with the exception of the projecting posterior lip of the actinos- 

 tome, flat; anal extremity obliquely truncated towards sloping actinal surface; 

 regularly arched from the edge of the test to the apex ; apex anterior, corre- 

 sponding nearly with the abactinal centre ; regularly arched from anal and 



