446 STKONGYLOCENTROTUS LIVIDUS. 



principal rows of tubercles, with two rows of smaller tubercles in the median 

 space. Miliaries and small secondaries covering closely the coronal platca 

 of both the ambulacra] and interamhulacral systems. Coronal plates broad, 

 with live vertical rows of tubercles extending from the ambitus towards the 

 abactinal region, forming nearly regular horizontal rows on each plate, the 

 central row of which is the longest. Plates densely packed with secondaries 

 and miliaries; spines short, stout, greenish, tipped with purple. Ocular 

 plates large; genital plates small, perforated by immense genital openings 

 placed <dose to the outer vd<j:i' : both these systems of plates carry small sec- 

 ondary tubercles extending over the anal system, which is made up of 

 small solid plates. Actinal membrane thin, covered by (dusters of well-sep- 

 arated plates in the continuation of the ambulacra! system. Actinal system 

 small. This species was originally described from a young specimen as a 

 Psammechinus. The irregularity of the third outside low of pores was noticed 

 at the time of making the description. A fuller series, containing larger 

 specimens, shows how they gradually lose this apparent arrangement in 

 three rows of pores: the irregular outer row, at fust separated by a vertical 

 row of small tubercles from the two inner rows, gradually forms, with in- 

 creasing age. an outer arc of two to three pairs of pores in continuation of 

 the inner arc. soon assuming the regular arrangement of pores character- 

 istic of the species or of Strong} locentrotus ; the two extremitiesofthe.se 

 arcs being separated by a vertical row of tubercles. 



Japan. 



Strongylocentrotus lividus 



! Echinus lividus I. am.. 1816, An. ?. Vert. 

 Strongyloceutrotus lividus 15u.. 1835, Prod. Dps. An. 



PL V.f. :j; PL XXIV. f. 2 r>. 



Test depressed, regularly arched. Abactinal system prominent, nearly 

 smooth, excepting a few irregular small secondaries and miliaries near the 

 anal system ; this is large, (dosed by one row of largo irregularly shaped 

 plates near the genital plates, and smaller rows of plates towards the anus. 

 In large specimens two ocular plates reach the anal system, all the others are 



