290 BULLETIN OF THE 



adult or greatly exaggerated. The ambulacral rosette is formed as in 

 Mellita and Echinarachnius by the independent growth of the upper 

 part of the ambulacra] area, which in Clypeastroids grows more 

 rapidly than the rest of the test, from the moment the pores are joined 

 by grooves, the {dates crowding upon one another, and pushing them or 

 part of them towards the edge of the test. In the Scutellae the pairs of 

 pores of the rosette are placed in the sutures of the ambulacral plates, 

 while in the Clypeastroids, besides the pair of pores in the sutures an 

 additional pair pierces the middle of each ambulacral plate. 



The development of Stolonoclypus prostratus and flat Clypeastroids 

 of the type of Clyp. placunarius is most instinctive, tending to show that 

 in connection with the development of the Scutellidae above described, 

 we must probably introduce a complete reform among the genera 

 recognized as Lenita, Scutellina, Runa, Echinocyamus, and other 

 minute Echinoids, which may eventually prove to be nothing but the 

 young of other Clypeastroids, as Mellita, Scutella, Laganum, Stolonocly- 

 pus, Clypeaster, Encope, and the like ; but want of sufficient material 

 prevents me from entering into this comparison more in detail. Though 

 we know now, from what has been said above, that the Scutellidae pass 

 through phases which cannot be distinguished from Moulinsia, Fibu- 

 laria, Runa, Scutellina, and the Clypeastroids proper pass, as I shall 

 show below, through a stage of growth identical with Echinocyamus. 

 For similar reasons I am inclined to consider Fibularia as the early 

 stage of some Clypeastroid. The absence of partitions in some species, I 

 think, cm easily be accounted for, as they are developed only later. We 

 have a species of Fibularia from the Sandwich Islands, in which there 

 are no partitions when very small, while in the adult these partitions 

 are most rudimentary. Greater material than I possess is necessary 

 to elucidate the affinity of the genus, which certainly has all the 

 features of immature Clypeastroids. 



Among the Echini, collected in great numbers by Mr. Pourtales, was 

 a small species showing, on careful examination, the facies of Echinocy- 

 amus, and which, after a minute comparison with Echinocyamus pusillus, 

 I could only distinguish from it, by its more circular outline, larger 

 tubercles, less crowded and thinner interior partitions; observing, how- 

 ever, in the horizontal sutures of the ambulacral plates, rows of minute 

 pores, extending from the imperfect rosette to the mouth, I at once 

 saw that it must be a young Clypeaster, and on comparing them with 



