398 ECHINODERMATA. ECHINIDES. 



on all sides like rays, sometimes prolonged to the mouth, and sometimes interrupted 

 before arriving at the margin. The retractile tubes which project from the small 

 holes are conceived some of them to be exercised in respiration, and the others for 

 locomotion, or for fixing the animal by acting as so many suckers ; but the spines also 

 contribute, at least in some species, to locomotion. The Echinides were included by 

 Linnaeus in one large genus, Echinus, which later naturalists have subdivided into 

 more precise groups. Lamarck divides the family thus : 



1. Anal opening above the margin, and dorsal. 



a. Anus dorsal and vertical ; shell regular. 



Gen. CIDARITES, ECHINUS. 



b. Anus dorsal, but approaching the margin. 



Gen. NUCLEOLITES, CASSIDULUS. 



2. Anal opening under the margin in the inferior disc, or on the margin. 

 * Mouth inferior, not central, but approaching the margin. 



Gen. SPATANGUS, ANANCHYTES. 

 ** Mouth inferior, always central. 



Gen. GALERITES, ECHINONEUS, FIBULARIA, CLYPEASTER, SCUTELLA. 



Gen. 5. CIDAIUTES, Lam. Echinus, Pall. 

 Body regular, spheroidal or depressed-orbicular, very rough ; 

 covering solid, testaceous or crustaceous, furnished with tu- 

 bercles perforated at the summit, upon which are articulat- 

 ed moveable spines ; five divisions radiating from the sum- 

 mit to the mouth, each bordered with two multiporous almost 

 parallel bands ; mouth inferior, central, armed with five os- 

 seous pieces ; anus superior and vertical. 



The Cidarites are distinguished from the Echini not only by their external aspect, 

 but by having the shell and the large tubercles pierced with holes for a muscular 

 chord which moves the spines. The compartments of the shell are also narrower 

 and more regular, and the spines are of two forms, some large and others very small. 



* Shell gibbous, subspheroidal, with waved compartments. 

 C. imperialis y Lam. Shell subglobose, depressed, the compartments 

 and the smaller spines purplish violet ; the large spines cylin- 

 drical, subventricose ; the apex striated and banded with white. 

 Inhabits Mediterranean sea D'Argenv. pi. J, fig. A. 



C. pistillaris, Lam. Shell subglobose, depressed, the larger spines 

 fusiform, subulate, and rough with sharp points, the neck sulcated, 

 and apex obtuse. Inhabits coasts of Isle of France Lam. iii. 55. 

 ** Shell orbicular, depressed, with the compartments straight. 



C. calamaria, Lam. Shell depressed-spheroidal, spinous and seti- 

 ferous ; the spines slender, smooth, fistulose ; transversely striat- 

 ed, and banded with white and greenish j fragile setae between 

 the spines. Inhabits Indian Ocean. Lam. iii. 58. 



C. diadema, Lam. Shell hemispheric, depressed, with five com- 

 partments, the centre warty ; spines long, bristly, subfistulose, 

 scabrous. Inhabits Indian Ocean. Lam. iii. 59. 



Gen. 6. ECHINUS, Lam. Lin. 



Body regular, gibbous, orbicular, globular or oval ; covering 

 solid, testaceous, furnished with imperforate tubercles, up- 



