CLARK: THE C1DARIDAE. 187 



Red Sea, Mauritius, the East Indies, and Australia is sadly needed. In the light 

 of such material I believe that additional species will be recognized, and it is quite 

 possible that the genus will need to be divided. For the present, however, I see 

 no better course than to let the genus stand as it is. It seems to be generally 

 agreed that Studer's ('80) Schleinilzia crenularis is a Phyllacanthus, probably 

 annulifera ; while the observations of Doderleiu ('87 and : 03) and de Meijere 

 (: 04) show that Ph. dubia Brandt ('35) and parcizpina Woods ('80) are appar- 

 ently synonyms of iinperirilis. The species designated au.itralis by Ramsey (05) 

 is apparently baculo-sa and Rhabdocidaris recens Troschel is clearly annulifera. 

 All of the recent species are littoral and are confined to the Indo-Pacific region, 

 but many extinct species have been described from Tertiary, Cretaceous, and 

 Jurassic strata of Europe and America. The following key to the living species 

 is based on the examination of only 118 specimens, but each of the five species is 

 represented by at least four examples. 



Key to the Species. 



Ambulacra very broad, .40 interambulacra or more; median area broad, 

 sunken and bare ; median interambulacral area also sunken and bare; 

 primaries seldom exceed h. d., provided with several whorls of vertical 



plate-like projections or flat, blunt thorns verticillata 



Ambulacra less than .40 interambulacra; median ambulacral and inter- 

 ambulacral areas not conspicuously sunken and bare. 

 Collar of primary spines without spots or longitudinal lines of deep red 

 or purple. 

 Coronal plates 5-6 (rarely 7); abactinal system small (.30-. 40 h. d.); 



actinostome large (.50-55 h. d.) imperialis 



Coronal plates 6-9 (rarely 10) ; abactinal system nearly equals or often 

 exceeds actinostome. 

 Primary spines stout 1.5-2.5 h. d., terete, slightly swollen above 

 collar, smooth, or with granules arranged in longitudinal series, 

 becoming ridges near tip ; no conspicuous thorns or pro- 

 jections thomasii 



Primary spines not as above, sometimes flattened at base, usually 

 with conspicuous thorns; collar smooth, reddish or purplish, 



unspotted annulifera 



Collar of primary spines with noticeable spots of purple or deep red, 



arranged in longitudinal rows and sometimes merged into lines . . baculosa 



Phyllacanthus verticillata. 



Cidarifes verticillata Lamarck, 1810, Anim. s. Vert., 3, p. 56. 

 Phyllacanthus verticillata A. Agassiz, 1872, Rev. Eel)., pt. 2, p. 151. 



Thite If, fisr. 3, Rev. Ech., A. Agassiz, 1873. 



This well-known and unmistakable species reaches a diameter of 35-10 mm. 

 The general coloration is dark brown and green, with the shades lighter in young 



