GENEEA AND GE0UP5) OE THE ECHINOIDEA. 261 



I'Alger. fasc. ix. p. 46, pi. iii. figs. 1-4, is not a satisfactory genus, 

 and there is little evidence of an internal or of a peripetalous 

 fascicle ; indeed, Humbert does not draw a subanal. It is 

 therefore not placed. If the fascioles were present, the genus 

 would be Lovenia (see p, 263), and if absent, Semipatagus 

 (p. 222). 



G-enus Echinooardium, Gray, 1825, Annals FJiil. p. 8 ; 1855, 

 Cat. Bee. Eeh. Brit. Mus. pt. i. p, 42. Loven, 1874, 

 Btudes, p. 55, pis. 3, 12, & 39 ; 1883, Pourtalesia, pis. 15, 17. 



Syn. Amphidetus, Agass. ; Amphidotus, Porb. 



Test moderate, thin, cordiform or oval in tumid marginal out- 

 line, gibbous, deeply and broadly grooved in front, truncated and 

 highest behind ; broader than high, rather flat dorsally in front, 

 high and broadly keeled behind the vertex, which is behind the 

 centre. Actinally with a tumid plastron projecting downwards, 

 a prominent labrum, and a sharp end to the plastron behind. 



Apical system at the termination of the abactinal groove, 

 excentric posteriorly, small, with four basals with large pores ; 

 the madreporite extending between and in the rear of the postero- 

 lateral basals ; the radial plates small. 



Anterior ambulacrum in the groove ; the pores small, single, and 

 irregular, or in pairs sometimes biserial or alternating where 

 included within the internal fascicle, and close near the apex, 

 where the tentacles have crenulated or stellate disks with a 

 central bulge and one or two large spicules. The pores are 

 larger and more distant anteriorly, where there are simple 

 locomotive tentacles with peripodia and penicillate tentacles, as 

 actinally. Lateral ambulacra in slight grooves, triangular in out- 

 line, widely open towards the apical system, where they are 

 limited by the internal fasciole, narrow distally ; the pairs of 

 pores large and not numerous ; the outer poriferous 2;ones form- 

 ing an arch with a slight discontinuity ; the tentacles branchial. 

 Actinally the ambulacra are plain and rather broad near the 

 peristome, but narrow on either side of the plastron ; the peri- 

 podia with capitate filaments. 



Peristome large, semilunar, with well-developed membrane- 

 plates, which are largest anteriorly, the anterior lip at a much 

 higher level than the posterior, which is pointed and blunt. 

 Spheridia exposed. 



Interradia narrow above, large actinally, all with a single 



