METALIA MACULOSA. 509 



extremity of the anterior lateral ambulacra, and a somewhat more decided 

 re-entering angle in the anterior lateral mterambulacral space. Genital 

 pores larger and more distant than in specimens of M. sternalis of the same 

 size. The petals are narrow, complete to the abactinal pole, with broad 

 poriferous zones ; the posterior petals longer than the anterior ones. Within 

 the peripetalous fasciole the plates carry large primary tubercles, arranged 

 in vertically distant, irregular, transverse rows in all the interambulacral 

 spaces. The whole anterior part of the test is covered by similar primary 

 tubercles, which diminish in .size as they extend towards the posterior lateral 

 interambulacra, below the fasciole, where the tubercles are small, crowded, 

 similar to those which cover the whole abactinal part of the test to the 

 ambitus. The actinal side is convex ; the actinal plastron narrow, elon- 

 gate, terminating in a prominent beak at the posterior extremity. The 

 subanal plastron is diamond-shaped, edged with a broad fasciole ; the bare 

 ambulacral avenues are broad ; the tubercles of the lateral interambulacra 

 and anterior part of the test are large, diminishing Aery gradually towards 

 the edge from the ambulacra. Those of the actinal plastron are large near 

 the actinostome, small towards the posterior extremity. 



The actinostome is large, somewhat broader than long. The anal system 

 is pear-shaped; the anal opening nearer the lower edge; the anal plates 

 numerous, polygonal, arranged concentrically, largest near the upper edge 

 of the system. Anal branch of fasciole does not reach the abactinal surface. 

 This species receives its name from the fact that the tubercles of the abactinal 

 surface do not entirely cover the coronal plates, but leave the edges more or 

 less bare ; the median posterior interambulacral suture is especially promi- 

 nent in dark-colored specimens ; the contrast between the bare and tubercu- 

 lated areas is very prominent. The color, denuded, is light violet; sutures 

 lighter colored, or of a light yellowish-brown tint. The spines are short, 

 curved, slender, light yellowish-pink. Those of the actinal side longer and 

 stouter, and on the actinal plastron flattened at the extremity. 



This species is closely allied to M. sternalis ; the principal differences are 

 its depressed test, its more central apical system, its narrow ambulacral 

 petals, and its well-separated posterior petals. The odd anterior ambula- 

 crum is flush with the test, except towards the ambitus, as it approaches the 

 fasciole, and below it. where it is placed in a slight indentation of the test; 

 while in M. sternalis we have a deep angular anterior groove, already 

 commencing; near the summit. 



