GENERA AND aEOIIPS OF THE ECHINOIDEA. 277 



Apical system slightly posterior, corresponding with the summit, 

 with four perforated basal plates ; and the madreporite is in the 

 right anterior, and passes backwards, separating the posterior 

 basals ; basal sutures obliterated. 



Ambulacra flush with the test, uniporous, increasing in width 

 to the ambitus and apetaloid, with but few plates, which are 

 large, high, and hexagonal. The areas diminish in breadth to 

 the peristome. The anterior ambulacrum appears to resemble 

 the others. 



The interradia have large plates and but few of them. 



Peristome excentric in front, broad, but short longitudinally, 

 more or less semilunar, and with a well-marked posterior lip 

 which projects. Plastron well developed, amphisternous and 

 tuberculate, contrasting with the broad plain posterior ambulacra 

 on either side. Periproct supramarginal, circular in outline. 

 There is a subanal fascicle only. 



Tubercles of the primary kind largest and most crowded at 

 the ambitus in all the areas, scattered over the test above the 

 ambitus, absent near the apex, and regularly placed in the odd 

 ambulacrum. Spines of actinal surface slender, club-shaped and 

 hollow, vdth a thick shaft. Ambulacral pedicels most powerful 

 and with small disks near the apex, and diminishing actinally. 

 Tufted pedicels around the peristome. 



Becent. (One species) Arafura Sea, 800 fms. 



Genus Cleistechintjs, P. de Loriol, 1882, Descript. dea 

 Ecliinides des Envio^ons de Camerino, Mem. Soc. PJiys. et 

 Sist. Nat. de Geneve., t. xxviii. no. 3, p. 27. 



The test is small, thin, depressed, tumid dorsally, oval, elongate, 

 rounded in front, where there is no notch, low and truncated 

 behind. 



Apical system probably disconnected ; the system is excentric 

 in front, and the only specimen observed has two genital pores 

 relatively large and very close. 



The ambulacra are composed of extremely small pores, barely 

 visible here and there. It is impossible to afGrm whether the 

 pores are single or in pairs. Ambulacral plates relatively very 

 large, so that there are almost as many ambulacral as interradial 

 plates. There is no anterior groove. 



The peristome has a posterior, projecting lip. The periproct 

 is oval, elongate, open at tlie summit of the posterior surface. 



