570 MARETIA PLANULATA. 



Maretia planulata 



Spalanrjui ovatus Lkkkk, 1778, Ki.. Add. (non Lamk. nee El.). 

 !Maretia /I'aiiula a GltAY, is."ij. Cat Rec. Ech., p. 48. 



[/• is, u- 

 PL XIX". f. 7-12; PL XXV. f. 8S-W, PL XXVI. f. >/. 22; PL XXX VI I. 



This is apparently one of the oldest species known, if 1 am correct in re- 

 ferring Leske's figure (Seba, III. PLXV.f. ::. :s) to this species, and it seems 

 astonishing that a species apparently so common should not have been fig- 

 ured by Selia. The figure he gives is tolerably characteristic, and certainly 

 appears to fit better M. planulata than Echinocard. flavescens to which it is 

 universally referred. In profile the flat test slopes very gradually from the 

 posterior edge to the vertex, which is somewhat above the anal system, and 

 arches regularly towards the sides. Excellent figures of this species have 

 been given by Michelin and by Martens. Test thin, depressed ; outline from 

 above slightly heart-shaped, rounded anteriorly, with n plight indentation at 

 the ambitus, made by the shallow anterior groove : this disappears somewhat 

 above the ambitus. The sides of the test are regularly rounded, slightly 

 angular, broadest in the central or posterior part of the test ; the posterior 

 interambulacral space extends beyond the general outline, forming a more 

 or less prominent, rounded keel, above the bevelled posterior anal extremity 

 of the test ; this slopes anteriorly. The large, pointed, longitudinally ellip- 

 tical anal system occupies the whole of the posterior extremity of the test ; 

 the subanal plastron is broad, somewhat heart-shaped, surrounded by a 

 narrow fasciole, frequently indistinct, or almost obliterated. This plastron 

 is on the edge of the test, partly on the actinal surface, and partly on the 

 bevelled portion of the posterior extremity. 



The apical system is small : four genital openings close together, anterior 

 to the centre. The poriferous zones of the broad petaloid lateral ambulacra 

 slope up to the edge of the somewhat raised broad interporiferous spaces; 

 the anterior ambulacra are the shortest The odd anterior ambulacrum is 

 flush with the test, except near the ambitus, where there is a slight groove ; 

 the pores are very minute, vertically distant, except near the apical system, 

 where they are closely crowded. In the lateral poriferous zones the inner 

 row is round, the outer elliptical, pointed ; they are connected by an indis- 

 tinct groove. The whole abactinal part of the test is covered by minute 

 secondary, perforate and crenulate, tubercles, very variable in size, quite 

 distant; the intervening space filled with miliaries. equally irregular in 

 size. In the lateral interambulacral spaces there are large, sunken, primary 



