﻿ON THE ECHINOIDEA. 



4(57 



ECHINOLAMPIDiE. 



Pygurus Hausmanni, Koch and Bunker. PI. XXXIX, XL to Supplement, p. 405. 



In all the specimens of this large ^ Hau * mannL 



urchin hitherto found it is the upper 



surface alone that is exposed. My 



friend, W. C. Strickland, Esq., having 



met with an uninjured test, he de- 

 termined to remove the matrix from 



the base, with the intention of showing 



the mouth- and vent-openings ; this he 



has succeeded in doing, and I am 



now, through his kindness, enabled to 



give a figure of the under surface and 



complete the description of this remark- 

 able species. 



The base is concave, inclining on 



all sides towards the mouth-opening, 



which is nearly central, being only 

 three tenths of an inch nearer the 

 anterior border ; the peristome is pen- 

 tagonal, and surrounded by five lobes, 

 which are moderately prominent ; the 

 ambulacral valleys are slightly de- 

 pressed, and converge in straight lines 

 to the mouth ; the wide inter-ambulacra 

 are convex near the margin, and, with 

 the depressed ambulacra, present a 

 series of gentle undulations throughout the under surface ; the anterior border is rounded, 

 without any trace of anteal sulcus ; the anal-opening lies in a deep, oblong depression near 

 the posterior border ; the test is very thin, and the tubercles in this region are very small ; 

 the apical disc is well preserved, and is only two lines in diameter ; the small ovarial plates 

 are closely soldered together, and covered by the madreporiform body which entirely 

 envelopes the disc, and appears like a central spongy button at the vertex ; the four 

 oviductal holes are visible, and alone indicate the extent of the plates ; the ocular plates are 

 not visible, mere depressions only showing their position. 



61 



