<)N THE FOUNG STAGES OF ECHINI. 741 



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 plates crowding upon one another, and pushing them, or a part of them, 

 towards the edge of the test (PL XII. f. w). In the Scutellidae the pairs 

 of pores of the rosette are placed in the sutures of the ambulacra] plates 

 (PI. XI. f. ,«), while in the Clypeastroids, besides the pair of pores in the 

 sutures, an additional pair pierces the middle of each ambulacral plate 

 (PI. XI. f. .<.;). 



The development of the flat Clypeastroids and of the Scutellidae as above 

 described is most instructive, showing that we must introduce a complete 

 reform among such genera as Lenita, Scutellina, Runa, Echinocyamus, and 

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

 the young of other Clypeastroids, probably of Mellita, Scutella, Laganum, 

 Clypeaster, Echinanthus, Encope, and the like ; but want of sufficient 

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

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

 through phases which cannot be distinguished from Moulinsia, Fibularia, 

 Runa, Scutellina. For this reason I am inclined to consider Fibularia as the 

 early stage of some Clypeastroid. The absence of partitions in some species 

 can, I think, easily be accounted for, as they are developed only in later 

 stages. We have a species of Fibularia from the Sandwich Islands, in which 

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

 partitions are most rudimentary. Greater material than I possess is neces- 

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

 of immature Clypeastroids. 



The young of Clypeaster subdepressus are pentagonal, with rounded 

 angles (PI. XIII f. 10); with increasing age (PI. XIII f. 16 -is) the con- 

 cavity of the lower side is more marked, the partitions increase from the 

 addition of needle-shaped processes, and they soon attain the shape and have 

 the structure given by Liitken in his figures of young Clypeaster subdepressus. 

 The tubercles increase more rapidly near the edge of the test, and a remark- 

 able feature of these stages is the presence of minute glassy tubercles similar 

 to those of Echinoneus, developing side by side with young tubercles, the 

 function of which is as obscure as it is in Echinoneus ; they are not found 

 in older specimens. 



The development of Echinolampas has thrown unexpected light upon the 

 affinities of the toothless Galerites and of the Cassidulidae. It shows con- 



