563 THE ANIMAL KINGDOM. 



and the test therefore cannot have been firm. Aristotle's lantern present. Anus 

 exocyclic only in Cystocidaris. Basal plates pierced by three to five, radials by 

 two, pores. Spines small as a rule, and restricted to interambulacra. 



2. Desmosticha (= Regulares, Endocydica] : of spheroidal or flattened circular 

 form. All ambulacra and interambulacra of equal length. Anus endocyclic. 

 Mouth central. Complex manducatory organs (Aristotle's lantern). Subdivided 

 into 



(a) Entobranchiata Cidaridae : devoid of external gills. Auricular arch 

 not complete and interradial. Ambulacral and interambulacral plates continued 

 on to peristome ; pores in straight rows ; pore plates primary and subequal. 



(b) Ectobranchiata : external gills present. Auriculae extend over the radii. 

 Interambulacral plates not continued on to peristome. (Saleniidae, Echinothuridae, 

 Arbaciadae, Diadematidae, Echinidae^] 



3. Clypeastroidea (= Exocydica in part) : shield shaped, often flattened. 

 Mouth central, with manducatory organs. Dorsal portion of five ambulacra 

 petaloid. Ambulacra of great breadth. Anus exocyclic. (Clypeastridae^ Scutel- 

 lidae^] 



4. Petalosticha (= Exocydica in part, Spatangoidea) : more or less heart- 

 shaped. Mouth more or less excentric ; no manducatory organs. Anus exocyclic. 

 Ambulacra petaloid, and anterior one often unlike the other four. Subdivided into 



(a) Cassidnlideae : oval, with mouth central or subcentral ; no petaloid 

 ambulacra or all petaloid. (Echinoneidae, Cassidulidae.} 



(b) Spatangideae : mouth excentric and transversely elongate ; a labrum ; 

 four ambulacra, petaloid as a rule; fascioles often present. (Collyritidae, Anan- 

 chytidae, Spatangidae.) 



General anatomical account, Kohler, Annales Mus. Nat. Hist. Marseilles, i. 

 1883. See also A. Agassiz, ' Revision of Echini,' Harvard Mus. Catalogue, No. vii. 

 pt. iv. or iii, 1872-74; Id. Challenger Reports, iii. 1881. 



Test, Zittel's Palaeontologie, Abth. i, Palaeozoologie, i. 1876-80. 



Classification of Desmosticha, Bell, P. Z. S. 1881. 



Cyanosoma urens, an Echinothurid, and its poison apparatus, Sarasin (C. F. 

 and P. B.), 'Ueber einen Lederigel,' &c., Z. A. ix. 1886. Pourtalesia, Lov^n, 

 Kongl. Sv. Ak. Handl. xix. No. 7, 1883. 



Pedicellariae, cf. lit. p. 194, and note, p. 558, ante. Sphaeridia, Ayres, Q. J. M. 

 xxvi. 1886. 



Structure of teeth, Giesbrecht, M. J. vi. 1880. 



Nervous system, Prouho, C. R., 102, 1886; Romanes, 'Jellyfish, Starfish, and 

 Sea-urchins,' Internat. series, 1885, cap. x.; Id. and Ewart, Ph. Tr. 172, 1881, 

 P- 835. 



Compound eyes in an Urchin (Diadema ?), Sarasin (C. F. and P. B.), Z. A. viii. 

 1884. 



Vascular system, points in dispute, Carpenter, Q. J. M. xxiv. 1884; xxv. 1885. 



Echinochrome or blood-colouring matter, MacMunn, Q. J. M. xxv. 1885. 



Pluteus of Dorocidaris, Prouho, C. R. 101, 1885. 



