NEOLAMPAS EOSTELLATA. 341 



external examination alone it would be difficult to trace the course of the 

 ambulacra, but from the interior [PL XVII. f. 11) we easily see one pore for 

 each ambulacra] plate, extending from the floscelle to the apical system, and 

 appearing as minute pores when seen from the outside ; through them pro- 

 trude very slender tentacles showing no trace of disk. In fact, the structure 

 of the whole of the ambulacra is identical with the structure of the part of 

 the ambulacra between the rosette and the mouth in other Echinolampadae. 

 The color of this Sea-urchin is yellowish-green, and I am convinced it is not 

 the young of any other Echinolamp, in spite of its size (14.7 mm ), owing to 

 the great development of the bourrelets, which in other Echinolampadae 

 appear only after the specific characters are fully formed and the main 

 features of the adult are attained. 



There is a peculiar structure of the ambulacra of Cassidulidae which seems 

 to have escaped notice thus far. The rosette is formed by two poriferous 

 zones, each containing two pores joined by a furrow. The poriferous zone, 

 which extends from the petals to the floscelle (mouth), is reduced to its sim- 

 plest expression, a single pore between two adjoining ambulacral plates ; it is 

 only the inner set of pores of the poriferous zone which extends to the mouth 

 in all the ambulacra ; the exterior pair does not go beyond the rosette. The 

 buccal membrane is bare, the mouth itself exceedingly minute. The bourre- 

 let between the floscelle is well marked by the crowded tubercles packed as 

 closely as they can be placed. The floscelle is well defined, consisting of 

 large elliptical pores ; there are only three of the inner set of pores. I was at 

 first tempted to regard this genus as the young of a new Echinolamp, on ac- 

 count of the absence of the ambulacral rosette. But having found in a young 

 Echinolampas the ambulacral rosette developed before the bourrelets, I take 

 it for granted that this species has the principal specific characters of the 

 adult, unless this genus forms an exception to all other Echini allied to it, 

 as in all young Clypeastroids, Spatangoids, and Echinolamps which I have 

 examined, long before we can tell with certainty to which genus the young 

 Echinoderm is to be referred, such an important character as the ambulacral 

 rosette is already well developed (Encope, Mellita, Echinarachnius), or at 

 any rate more prominent than the remaining portion of the ambulacral 

 system. 



From 100- 125 fathoms. 



