244 



PHYLUM ECHINODERMATA. 



processes tall, narrow, two on each ambulacrum, fitting in below the jaws. 

 Genital pores sometimes outside the apical system (see p. 218). 



Clypeaster Lamk. (Fig. 172), Red Sea, Indian Ocean and warmer seas 

 generally ; Diplothicanthus Duncan, Plesianthus Duncan, all recent and 



fossil ; Anomalan- 

 thus J. Bell, r. 



Fam. 3. Laga- 

 nidae. Test flat ; 

 petals unequal, nar- 

 row, lanceolate ; 

 ambulacra beyond 

 them very wide ; 

 pore-pairs for bran 

 chial tube-feet few, 

 and between them 

 are minute pores 

 for prehensile ten- 

 tacles. Interradii 

 small, continuous ; 

 each with a single 

 apical and peristo- 

 mial plate. Peri- 

 proct between the 

 peristome and pos- 

 terior margin. Peri- 

 gnathic processes 

 single on the inter- 

 radial peristomial 

 plates, situated so 

 as to be beyond not 

 below the jaws. 

 Lagdnum Klein, r 

 and f. 



Fam. 4. Scutel- 



lidae. Test very flat, often lobed or perforated. Ambulacra! furrows on 

 lower side bifurcating and branching (pore-fasciae] ; small pores on actinal 

 surface only found in furrows. Radiating partitions internally. Scutella 

 Lamk. (Fig. 157), fossil ; Echinarachnius Leske, r ; Echinodiscus Brey r 

 nius, f and r ; Encope L. Ag., f and r ; Mellita Klein, f and r ; Lenita 

 Desor, f ; Mortonia Desor, f ; Rotula Klein, r ; Arachnoides Breynius, 

 f and r. 



Sub-Order 5. SPATANGOIDA (Heart-urchins). 



Test often more or less heart-shaped. Mouth central or subcentral, or 

 at the front end of the lower surface of the shell. Anus outside the apical 

 system in the posterior interradius (Fig. 153). External gills, jaws, 

 teeth and perignathous ring absent. The plates of the shell are not con- 

 tinued on to the peristome. Sphaeridia present. Large spines are never 

 found. Fascicles and clavulae are frequently present. There is usually an 

 ambulacral rosette on the upper surface ; sometimes with only four petals, 

 the anterior ambulacrum not being petaloid. 



When the mouth is shifted in the direction of the anterior radius, it is 

 transversely elongated and possesses on its hinder border a lip formed by 



FIG. 172. Clypeaster rosaceus (E^ne animal). 



