132 PEor. p. M. dtjncan's revision or the 



Apical system large, madreporite large, and in the largest 

 basal plate (No. 2) ; some radial plates enter the periproct. 



Ambulacra broad, with numerous, low, compound plates ; 

 poriferous zones broad, the pairs numerous, close vertically, but 

 moderately far apart in the slightly inclined arcs or straight and 

 horizontal series of three pairs. The plates as in Tripneustes, but 

 slightly higher and narrower. Small tubercles in the poriferous 

 zones ; interporiferous areas with several vertical rows of mo- 

 derately large primary tubercles, diminishing in number above 

 the ambitus. 



Interradia with numerous rows of plain, primary tubercles 

 resembling those of the ambulacra, diminishing in number 

 apically. A more or less bare space on either side of the 

 median ambulacral and interradial lines near the apical system. 



Peristome large, with deep and long incisions for the branchiae, 

 the edges turned up. Pedicellarise very large. Spines small, 

 striated. 



Becent. Mauritius, East Indian Islands, Pacific Islands, 

 Panama. 



The alliance to Tripneicstes is close, the main distinctions 

 being the shape and the concave actinal surface with its large 

 well- cut peristome ; the poriferous zones are also narrower in 

 Boletia and a more arched arrangement of pairs occurs, remote 

 from the ambitus, where the structure of the ambulacral plates is 

 as in Tripneustes ; there are no double plates, however, as in the 

 fossil Tripneustes. 



Genus Tb,ip]o;ustes, Agassiz, 1841, Introd. to livr. 2, Monogr. 

 d^Ech. viv. et foss. p. 7; also 1841, Monogr. d'Ecli. viv. 

 et foss. livr. 4, Preface to Yal. Anat. d'Ecli. p. viii. Desor, 

 1858, Stjnopsis, p. 132. Liitken, 1863 (pub. 1864), Vid. Medd. 

 f. Nat. For. i. Kjob. p. 95. A. Agassiz, 1872-4, Revision., 

 p. 301.^ J. Bell, 1879, Froc. Zool. Soc. p. 655. De Loriol, 

 1883, Ech. de Vile Maurice, p. 25. Duncan Sf Bladen, Fal. 

 Ind. ser. xiv., Foss. Ech. W. Bind, pt. v. jd. 310, pis. 48, 49. 



Syn. Sipponoe, Grray, MSS. name, 1840 ; HeliecMnus, Girard. 



Test moderate to very large, thin, tumid, circular or sub- 

 pentagonal in outline, broader than high, often subconical, 

 tumid around the peristome ; may be depressed and concave 

 around a sunken apical system, with or without depressed inter- 

 radial median areas abactinall3^ 



