GENERA AND GEOUPS OF THE EOHINOIDEA. 51 



Subgenus Pseudocidaeis, JEtallon (genus), 1859, Letheea Brunt. 



p. 3313. Cotteau, 1882, Bull. Soc. Zool. de France, vol. vii. 



p. 1. De Loriol, 1887, Bee. Zool. Suisse, vol. iv. p. 336, 



pi. XV. figs. 2-" 5." 

 Ambulacra very undulating abactinally, narrow, with primary 

 tubercles only near the peristome, granules elsewhere. Inter- 

 radia broad, with few coronal plates, and two vertical rows of 

 large primary tubercles, distant. Spines large, massive, cylindroid 

 or fusiform, or pear-shaped, striated longitudinally or granular. 

 Fossil. Oolite and Cretaceous : Europe, N. Africa, Mexico. 



The genus Aster ocidaris, Cotteau, 1859, has all the characters 

 of Hemicidaris, and it appears that the existence of star-shaped 

 or triangular bare spaces in the median interradial areas near 

 the projecting basal plates is not of generic importance. Astero- 

 cidaris should be placed as a subgenus of Semicidaris, with the 

 following characters : — 



Subgenus Asteeocidaeis, Cotteau, 1859 (genus), Bev. et Mag. de 

 Zool. ser. 2, vol. xi. p. 159. 



Apical system large, with basal plates projecting adorally into 

 a bare median interradial space ; interradial plates ten or less in 

 number in each vertical series. 



Fossil. Europe. 



Genus Aceocidakis, Agassiz, 1840, Ech. Foss. de la Suisse, pt. ii. 

 p. 10. JDesor, 1858, Synopsis, p. 83. 



Test large, tumid at the ambitus, and subcorneal or spheroidal 

 dorsally, ilat actinally. 



Apical system small, some or all of the basal plates with a 

 large perforate tubercle, the madreporite large. Periproct large. 



Ambulacra straight, broad at the ambitus, with two vertical 

 rows of large perforated primary tubercles, slightly smaller than 

 those of the interradia, and extending to the apex ; pairs of pores 

 uniserial and in simple series near the apex, in arcs of from four 

 to seven pairs near the larger tubercles, crowded and polyserial 

 actinally ; plates " diadematoid," with some additional components; 

 sutural lines as grooves on the flanks of the tubercles. 



Interradia with two vertical rows of large primary tubercles, 

 ouly the largest being perforate and crenulated. 



