184 SYNOPTIC COLLECTION. 



Sometimes the ambulacral petals take up the greater 

 part of the upper surface of the corona, as is the case with 

 Echinanthus rosaceus Gray (Nos. 338-340). The central 

 portion of each petal is raised while the furrows of the 

 pore-bearing zones are sunken, making the rosette most 

 conspicuous. Here, as in Clypeaster, the madreporic 

 body is in the center. Joined to it are the ocular plates 

 perforated for the ocular pores (not seen in No. 339), 

 while beyond it are the genital plates with their openings 

 (No. 339). The spines of this genus are small as are 

 most of the Clypeastroids. When removed as in No. 339 

 the tubercles are seen to be much reduced in size from 

 the regular urchins. The vertical section (No. 340) ex- 

 hibits the powerful jaws and the massive pillars of the 

 interior. 



Not only are the upper and lower portions of the test 

 united by pillars but in Laganum depressum Less. (No. 

 341), there are walls running parallel with the margin, as 

 seen in the cross section (No. 342). In this genus the 

 edge is much thickened, and the anus is on the lower side 

 quite near the mouth. 



The young Echinarachnius parma Gray, varies in form, 

 but in No. 343 it is circular and somewhat dome-shaped, 

 while in other specimens it is elliptical. No. 343, a-e, 

 has light colored spines attached. There are two rows 

 of these on both the ambulacra and interambulacra. They 

 are short and delicate, very different from the long spines 

 of the primitive and embryonic regular sea urchins. The 

 youngest specimen (No. 343, a) is without a distinct am- 

 bula'cral pattern, and the ambulacral grooves of the lower 

 surface are scarcely visible. In an older specimen meas- 

 uring 5.1 mm. these grooves have been seen, and accord- 

 ing to A. Agassiz minute pores were formed in them. 



The mouth is near the middle of the lower side pro- 

 tected by spines above (No. 343, c) and sunken within 

 the corona are the five horizontal teeth. The anus at 

 this stage is on the upper side a short distance from the 



