ON THE ECHINOIDEA. 



407 



ECHINOLAMPID^. 



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



In all the specimeus of this large Tygums Hausmanni. 



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 fines 

 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. 



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