602 METALIA STEENALIS. 



petalous fascicle, the whole abactinal part of the test is covered by small, 

 distinct tubercles, perforate and crenulate, with large, flat, indistinct scrobic- 

 ular circles, and but few miliaries scattered between. On the actinal side 

 the tubercles increase rapidly in size towards the ambulacra, where they 



attain their greatest size, and are quite distant ; the tubercles of the actinal 

 plastron diminish rapidly from the edge to the median keel. 



The tubercles of the posterior part of the subanal plastron increase in size 

 from the outer edge ; they run in curved radiating lines towards the middle 

 transverse line, from which the rows of tubercles radiate towards the ante- 

 rior edge, becoming smaller, and forming more numerous rows as they 

 approach the fasciole, between the deeply sunken pores, which arc placed 

 adjoining the fasciole, and from which slight grooves extend between the ra- 

 diating rows of tubercles. These large specimens show, perhaps, better than 

 in any other Spatangoid 1 have had occasion to examine, that the pores 



of the subanal plastron art' formed by the posterior poriferous zones of the 

 posterior lateral ambulacra. 



In smaller specimens, which have been described as Xauthob. Garetti, the 

 • is more globular, swollen ; the outline of the posterior interambulacrum 

 regularly arched ; the posterior extremity vertically truncated. The poste- 

 rior petals arched outwards: only a small part of the abactinal part of the 

 posterior zone rudimentary. The peripetalous fasciole but slightly sinuous, 

 and re-entering little in the lateral interambulacra. The actinal side quite 

 convex, and the subanal plastron placed entirely on the vertically truncated 

 posterior extremity. It is comparatively more diamond-shaped, nearly as 

 high as broad'; the broadest part of the fasciole i< on the sides in this stage 

 of growth. The spines are short, slender, cylindrical, slightly curved, of 

 uniform size on the abactinal surface, except adjoining the edge of the 

 petals within the peripetalous fasciole, and on the sides of the odd anterior 

 ambulacrum. On the lower side they are longer, but otherwise not different. 

 They are. in dried specimens, of a brilliant straw-color; in alcohol the color 

 is more grayish. 



Aery small specimens do not differ essentially from the above ; the pos- 

 terior ambulacral petals are straight, well separated to the apex by the inter- 

 vening interambulacral space ; the posterior petals are relatively shorter, 

 and the peripetalous fasciole scarcely forms a re-entering curve within the 

 lateral interambulacra. The subanal plastron is as high as broad, diamond- 

 shaped. An excellent series of specimens of all sizes, collected in New 



