252 CIDARIS. 



drawaJ of the Galerites, still contains the Clypeastroids. From the structure 

 of the ambulacra! system, they have some affinity with the Spatangoids ; 

 yet the presence of partitions and teeth, combined with petaloid ambulacra, 

 seem to constitute good subordinal characters for the Clypeastroids as con- 

 trasted with the Spatangoids proper, which include all the edentate forms, 

 taking in also the edentate genera formerly placed among Galerites, as well 

 as the Cassidulidae, sometimes regarded as independent suborders. 



CIDARIS. 



Cidaris Ki.k.ix, 1734. Nat Disp. Echin. 



Test thick, circular, turban-shaped ; actinal and abactinal region equally 

 flattened ; ambulacra narrow, undulating, having only granular tubercles ar- 

 ranged in vertical rows rarely more than six ; poriferous zones narrow, form- 

 ing a single vertical row of contiguous, disconnected pores. Interambulacra 

 from three to five times as broad as the ambulacra, with but two vertical rows 

 of primary tubercles ; these arc few in number, rarely going beyond seven in 

 each vertical row in the largest specimens. They are surrounded by large 

 scrobicular circles, either elliptical or circular. Areola more or less sunken 

 beneath the concave miliary zone ; granular tubercles occupy the whole of 

 the coronal plates between the scrobicular circle ; the primary tubercles 

 are perforated with a smooth base in all recent specimens. 



The abactinal system is large, flat; composed more or less of pentagonal 

 genital plates, nearly uniform in size separated by triangular or crescent- 

 shaped ocular plates. The anal system is pentagonal, with larger plates in 

 angles of pentagon between genital plates. 



The primary spines are large, stout, cylindrical, club-shaped, more or less 

 fluted, often surpassing the diameter of the test in length, and the granula- 

 tions assuming only a longitudinal linear arrangement. 



The name Cidaris dates back to Klein, but he as well as Leske used 

 Cidaris to denote what corresponds to the Echini regulares. The first limita- 

 tions were made by Lamarck, and his species of Cidarites correspond to the 

 Cidaridae of Midler and Diadematidae of Peters. The genus has been subse- 

 quently modified by Gray, Brandt, Agassiz, Desor, Cotteau, and A. Agassi/.. 

 For the sake of convenience, we can separate into two categories the spe- 

 cies of Cidaris, those with crenulated base and those with a smooth base. 



