MARETIA ALTA. 569 



Maretia alta 



! Maretia alta A. Ac. 1SG3. Pi-oc. Ac. N. S. Phila., p. 360. 



The outline from above is elliptical, rounded anteriorly, with a slight inden- 

 tation at the ambitus formed by the shallow anterior groove. Posterior ex- 

 tremity truncated, nearly vertically, across the extremity of the petals. Seen 

 in profile, the test is uniformly rounded from the anterior edge to the apical 

 system, and rises gradually to the vertex, which is slightly anterior to the 

 truncated posterior extremity. The test slopes regularly from the central line 

 to the lateral edges of the test. Apical system anterior. Petals narrow, lan- 

 ceolate, extending nearly to the edge of the test. Anterior poriferous zones 

 of the anterior lateral ambulacra obliterated, with the exception of three or 

 four outer pairs of pores. Anterior odd ambulacrum narrow, reduced to a few 

 vertically distant pores, flanked near the apical system by a few larger pri- 

 mary tubercles ; the rest of the abactinal surface, with the exception of a 

 few large primary tubercles near the edge of the test in the posterior lateral 

 interambulacra, is covered by minute, closely crowded secondary tubercles, 

 carrying short, slender, curved spines. On the actinal surface the tubercles 

 increase in size towards the bare ambulacral avenues, and are arranged diag- 

 onally, carrying proportionally longer and stouter spines. The actinal plas- 

 tron extends half-way to the actinostome from the subanal plastion, forming 

 a sharp beak at its posterior edge. The subanal plastron is heart-shaped, 

 placed entirely within the truncated posterior extremity, surrounded by a 

 broad fasciole, which extends to the lower edge of the large transversely 

 elliptical anal system, placed at the upper edge of the truncated posterior 

 plane. 



The proportions of the anal system, of the subanal and actinal plastron, 

 with the beak at its posterior edge, and the high test readily distinguish this 

 species from M. planulata. " Of a light buff color above, radiated with rows 

 of flesh-colored patches " ("W. Stimpson). No large specimens of this species 

 have yet been found. 



Width 

 Long. Trans. Subanal 



Diaui. Diam. Height. Plastrun. 



20.3 16. 10. 7. 



Japan. 



