16 



PANAMIC DEEP SEA ECHINI. 



A comparison of the shape of the coronal plates of P. Cohosi of speci- 

 mens of different stages of growth shows that with increasing size the 

 coronal interambulacral plates — let us take the fifth plate of the left 



10 nun. 



Fig. C9. 

 Figs. 38-40. Porocidarts Cobosi 



anterior interambulacrum adjoining the odd ambulacrum — become grad- 

 ually wider; in a young specimen of 8 mm., Fig. 38, the fifth plate is high, 

 shglitly narrowed at the abactinal suture (PI. 10, fig. 4), the primary 

 tubercle occupying nearly the whole of the plate which carries but three 

 secondaries and three miliaries. In a specimen of 10 mm., Fig. 39, the 

 plate has become less high compared to its width, and carries only one 

 additional miliary. In a somewhat older stage, 18 mm., Fig. 40, the area 



m 



on the aml)ulacr.'\l side of the primary tubercle has become still wider, 

 and the secondaries seem to be arranged in sets of threes, not only in this 

 stage, but also in a specimen of 21 mm., Fig. 41 (PI. 10. fig. 7), and one of 

 35 mm., Fig. 42 (PI. 10, fig. .9). The independence of the growth of the 



