CIDARID.E. 



7 



of the splitting of two of the plates of the second series which have reached 

 the genital ring, the plates of the different series present a remarkable 

 uniformity. 



In Doroeidaris panamensis we have, as in P. Cobosi, quite regular stages 

 in the growth of the second and third cycles of anal plates. In a young 

 specimen of 10 mm., Fig. 22 (PI. 3, fig. l), we have the five large primitive 



10 mm. 



Fie. 22. DoRociDARrs panamensis. 



IS mm. 

 Flu. 23. DOROCIDARIS PANAMENSIS 



anal plates in the sutures leading to the ocular plates; two of the plates are 

 separated by large secondaries ; the others are merely somewhat wedged 

 apart by the secondaries near the anal opening. In a somewhat older 

 specimen of 18 mm., Fig. 23 (PI. 3, fig. 2), the primary plates are separated 



30 mill. 



Fig. 24. Dokocidaris panamensis. 



2S mm- 



Fio. 25. Centrocidakis Doederleini. 



by secondaries all of nearly uniform size, one of the plates of the third 

 cycle having also reached the genital ring. In a specimen of 30 mm. 

 (PI. 3, fig. 3) the arrangement of the anal plates is not materially different, 

 Fig. 24. The arrangement of the anal plates is the same in a specimen of 

 Centrocidaris Doederleini of 28 mm., Fig. 25 (PI. 5, fig. 4). 



