222 PEOF. P. M. DTJJiTCAN S RETISION OF THE 



aborted more or less ; tlie paired ambulacra with subequal petaloid 

 parts, in deep, straight, or slightly flexuous grooves closed, the 

 anterior pair more divergent than the posterior, not expanding 

 but very equal in breadth. 



Peristome very excentric in front and close to the notch, large, 

 transverse, semilunar, and with a strong posterior labrum. Peri- 

 proct large, elliptical, transverse, supramarginal, in the small 

 truncation. Tuberculation very small. No fascicles. 



Fossil. Miocene : Australia (see also Quart. Journ. Greol. Soc. 

 1887). 



Grenus Hemipatagus, Desor, 1858, Synopsis, p. 416, pi. xliv. 

 figs. 4-5. Cotteaio, 1863, Ech.foss. d. JPyren. p. 150. 



Syn. Tuberaster, Peron & G-authier. 



Test small, cordiform, rather high, highest at the posterior 

 truncation, as long as broad, tumid above, notched anteriorly, 

 flattish actinally. 



Apical system with four perforated basal plates ; the madre- 

 porite central and extending posteriorly, and separating the 

 postero-lateral basal plates. 



Ambulacra diverse, the anterior with small pores, and the 

 lateral petaloid, long, and comparatively flush, with sunken pori- 

 ferous zones. Several large perforate and crenulate primary 

 tubercles, in deep scrobicules, wide apart, in the lateral interradia 

 abactinally. 



Peristome semilunar, with a projecting posterior labrum ; the 

 amphisternum broad, smooth, and worn-looking. Periproct 

 posterior, supramarginal. Fascicles absent. 



Fossil. Eocene : Europe. Tertiary : Asia and Java. Pliocene : 

 Europe. 



Grenus Plattbeissus, Gruhe, 1865, Jahresh. d. ScJiles. Ges. f. 

 Vaterl. Cult. p. 61. A. Agassiz, 1873, Revision, p. 562. 



Test moderate, depressed, elliptical, and somewhat rounded in 

 the thick ambital outline, tumid dorsally, flat actinally. 



Apical system excentric in front, small, with four perforated 

 basal plates, compact. 



Ambulacra diverse, flush, the anterior with very few pairs of 

 small pores ; the lateral petaloid, but open at the ambitus, narrow ; 



