CORONA AND PERISTOME OF ARCHMOCIDARIS WORTHENI. 217 



The interambulacral plates of Arcliseocidaris loortheni have a large cen- 

 tral perforated primary spine "tubercle which bears a long smooth spine 

 measuring from about 5 to 6.5 centimeters in length. In addition there 

 is on the borders of the plates a row of small secondary spine tubercles. 

 In plate 8, figure 43, by a mistake of the artist (see foot-note, page 216), 

 the secondary spine bosses are too numerous and too prominent in each 

 plate. They are represented more correctly for this species in the recon- 

 struction (plate 8, figure 44). The spines belonging to these small tuber- 

 cles have never been described in the genus. A specimen of Archseocidaris 

 wortheni in the Museum of Comparative Zoology (catalogue number 

 3028, plate 8, figure 46), besides the large primary spines, shows the 

 small secondary spines associated with the small tubercles on the borders 

 of the plates. These small spines are smooth, acicular and measure from 

 2 to 2.4 millimeters in length. The enormous disproportion in size 

 between the primary and secondary spines is shown in the figure, 

 although from lack of space the entire length of a primary spine could 

 not be given. The dotted lines in the figure represent a reconstruction 

 of the primary spine from another specimen, the spine belonging to the 

 plate figured, terminating by a fracture. Similar secondary spines are 

 also shown in a specimen of Archseoddaris agassizii in the Museum of 

 Comparative Zoology (catalogue number 3037). 



The choice specimen of Archseocidaris tvortheni described (plate 8, figure 

 43) not only has the ventral row of plates of the corona preserved almost 

 entire, but also has the buccal pyramids and plates on the peristome 

 preserved as well.^ The pyramids lie opposite the interambvilacra in 

 each of the 5 areas. The pyramids of each area consist of two parts, as 

 indicated by the median suture. While in contact when well preserved, 

 the parts may become separated. The pyramids in this specimen are 

 truncated orally as shown in the figure, but in other specimens, as seen 

 in the American Museum and in a specimen of this species (catalogue 

 number 3027) in the Museum of Comparative Zoology, they are bluntly 

 acuminate orally. In one area, A^ of the figure one side of a pyramid 

 is restored as indicated by dotted lines ; otherwise the outlines are ex- 

 actly as in the specimen. The teeth, which should lie at the oral termi- 

 nation of the pyramids and between their apposed tips, are not preserved. 



On the peristome the plates of the interambulacral areas are scale-like, 

 imbricating adorally (plate 8, figure 43). The plates are largest on the 

 outer border of the peristome and decrease in size toward the oral area, 

 where also the number of plates is relatively less. These plates do not 



*In Professor Hall's original figure, as cited, the pyramids are shown, though I have been able 

 to add something in regard to them. The plates on the peristome, however, are only indicated 

 by a few dots showing no details. 



