204 THE ATLANTIC. [chap. iv. 



three times its width near the base, and three times the diame- 

 ter of the disk. Tlie marginal plates are long and narrow, run- 

 ning up with a slight curve outward from the edge of the am- 

 bulacral groove until they meet the border of the dorsal perisom 

 above. They are closely set with short bhmt spines, which be- 

 come gradually a little longer toward the radial groove ; and 

 at the edge of the groove each plate bears a tuft of about six 

 rather long spines : these tufts in combination form a scalloped 

 fringe spreading inward on each side over the groove. The 

 dorsal surface of the body is covered with a tessellated pavement 

 composed of capitate paxilli. The heads of the paxilli in close 

 apposition combine to form a mosaic with rudely hexagonal 

 facets ; and as they are raised upon somewhat slender shafts, 

 whose bases, like the plinths of columns, rest upon the soft per- 

 isom, arcade-like spaces are left between the skin and the upper 

 calcareous pavement. The eggs pass into these spaces from the 

 ovarial openings : on bending the perisom and separating the 

 facets, they may be seen in numbers among the shafts of the 

 paxilli. There is a continual discharge of ova into the passages, 

 so that eggs and young in different stages of development oc- 

 cupy the spaces at one time. The young do not escape until 

 at least six ambulacral suckers are formed on each arm ; they 

 may then be seen pushing their way out by forcing the pax- 

 illi to the side, and squeezing through the chink between them. 

 While it is extricating itself the oral surface of the young is al- 

 ways above, and the centre of the star with the mouth is usu- 

 ally the part which first protrudes ; then the arms disengage 

 themselves one after another, many of the brood remaining for 

 a time with one or two arms free and the others still under the 

 paxilli. When the young have become disengaged, they re- 

 main for a considerable time attached to the parent by the cen- 

 tre of the dorsal surface. I could never satisfy myself by what 

 means this is effected ; the attachment is very slight, and they 

 are removed by the least touch. In this attached stage until 



