Klem — Revision of the Palaeozoic Palae'echinoidea. 8 



are perfect. The statement of Jackson and Jaggar that areas 

 showing three plates ventrally should be considered incom- 

 plete ventrally, and that, ** when well preserved show at the 

 oral termination angles for the articulation of the lower most 

 missing row," * is easily refuted. When examining perfect 

 specimens, I have always found that immediately below the 

 three lowest plates were the teeth, thus precluding any possi- 

 bility of any plates having fallen out. 



The same gentlemen assert further that the lower row of 

 plates does not really represent the initial plate, but that it 

 was a single plate, which, by the encroachment of the en- 

 larged actinostome, was gradually reabsorbed . As conclusive 

 evidence they make the following statement : t ' * In a speci- 

 men of Melonites multiporus in Yale University Museum 

 (diamond number 157, specimen C) we find an important fea^ 

 ture bearing on the above consideration. In this specimen 

 (plate 3, fig. 10) the two ventral plates have each an angle 

 toward the median line, and these together with the straight 

 edges of the bottom enclose a triangular space which doubt- 

 less contained the single initial plate, as in a similar stage of 

 Strongylocentrotus . This specimen of Melonites does not 

 actually show the initial single plate, and obviously in its pe- 

 culiar position it would easily drop out after the death of the 

 individual or in the processes of fossilization. To our minds 

 the angles for its reception are almost as strong evidence as 

 the plate itself." 



I see no proof from the figure that the plates numbered 1 

 and 2 were the terminating plates and no reason to assume 

 that the initial plate was triangular. Taking the drawing as 

 given on pi. 3, fig. 10, we can increase the number of 

 plates ad libitum, simply by completing the hexagons. Why 

 should we assume that the initial plate was triangular, 

 when perfect specimens show clearly that there were three 

 and that they were pentagonal or hexagonal? Furthermore, 

 if resorption took place (which I doubt very much) by what 

 law of nature could the plates twist themselves from the 



* BuU. Geol. Soc. Amer., vol. 7, p. 143. 

 t Bull. Geol. Soc. Amer., vol. 7, p. 144. 



