PERISCHOECHIXIDAE. 



647 



The teeth of Archaeocidaris were first figured by Miinster (Beit. PL III. J. 

 6 d ) ; by Desor (Synopsis, p. 154). in 1856, and attention was called to them 

 by Miiller in 1857 ; he figured the teeth. Hall, on Plate 26 of his Iowa Re- 

 port, gives figures, showing the existence of jaws in Archaeocidaris Worthenii, 

 though in the text no attention is paid to this. Meek and Worthen have 

 given (in Vol. II. of the 111. Geol. Rep., p. 227, Fig. 21) a cut (Fig. /), show- 

 ing the presence of teeth in Melonites raultipora, the furrow in the centre of 

 the teeth resembling that of the teeth of Archaeocidaris figured by Miiller. 



Fio. 1. 



Fig. 



Fig. 6. 



The figures given by Meek and "Worthen, p. 228, Vol. II., 111. Geol. Rep. 

 Figs. 21, 22 {Figs. 5, 6) are most interesting ; they agree entirely with the 

 general structure of the apical disc of Echini, showing ocular and genital 

 plates and a large anal area. The genital openings are more numerous, and 

 there is apparently no madreporic body described, though the presence of an 

 unequal number of pores in the different plates may indicate the presence 

 of such a body ; the larger one being probably a madreporic body, as sug- 

 gested bv Meek and Worthen. The presence of two genital openings is not 

 an uncommon feature in recent Cidaridae. I cannot agree with Meek and 

 Worthen in considering the differences in the apical structure as sexual, to 

 judge at least from analogy. In our common Sea-urchins the difference in 

 the sexes can be determined only at the time of spawning by a slightly dif- 

 ferent coloration, and there is nothing in the shape of the genital plates or in 

 the size and number of the genital pores which indicates a sexual difference. 



Fig. 1. Oral opening (somewhat distorted), and jaws of Melonites multipora (natural size), d d d, 

 spaces between teeth (foramen of the pyramid ?).* 



Fig. 5. Apical disc of Melonites multipora, showing the anal opening, surrounded by the genital and 

 ocular plates, and their connection with the ambulacra] and interambulacral pores (two diameters). 



Fig. 6. Melonites multipora, having five pores in three genital plates. 



* I have to thank Messrs. Worthen and Meek for allowing me to copy their cuts, illustrating a few of 

 the principal points of the genera here mentioned. 



