ECIIIXOTIIUIMD.K. 



147 



TABLE OF THE MORPHOLOGICAL CHARACTERS OF THE ECHINOTIIUR1H i: 



AND DIADEMATHXE. 



Structure of 



Ambulacra. 



Interambulackal 



Areas. 



Primary Tubercles. 

 Abactinal System. 



ACTINOSTOME. 



Teeth. 

 Jaws. 



Perignathic 



Girdle. 

 Arrangement of 



Tube-feet. 



Spines. 



Stewart's Organs. 



Gills. 

 Alimentary Canal. 



Pedicellari.e. 

 Globiferous. 

 Ophicephalous. 



Triphyllous 



Tridentate. 

 Tube-feet. 



Spileridia. 



Calcareous 

 Spicules. 



Color. 



Size. 



Diadematid.e. 



Diadematoid ; each compound plate 

 consists of a middle primary, and 

 abactinal and actinal .secondary ele- 

 ments. Adoral imbrication usually 

 slight or wanting. 



Interambulacral plates bevelled on 

 edge. 



Primordial interambulacral plate re- 

 sorbed. Aboral imbrication not 

 usually noticeable. Without evi- 

 dent membranous interspaces. 



Perforated ; usually crenulated. 



Large; anal system covered by nu- 

 merous small plates ; anal tube often 

 present; commonly 2-5 oculars in 

 contact with anal system; genito- 

 ocular ring continuous, with rare ex- 

 ceptions ; genital plates seldom split. 



With five pairs of buccal plates and 

 more or less numerous small scat- 

 tered plates, either confined to, or 

 much more conspicuous in the am- 

 bulacral areas. 



Grooved. 



More or less erect, with open foramen 

 magnum. 



Continuous; auricles and apophyses 

 more or less extensively developed. 



In three longitudinal series, com 

 monly; sometimes in two; rarely 

 in one actinally. 



Hollow; long, usually verticillate, 

 sometimes smooth; hoofs and con 

 spicuous skin-sheaths wanting. 



Rudimentary or usually wanting. 



Well-developed. 

 Long and large; oesophagus long and 

 more or less coiled. 



Wanting (except Centrostephanus). 



Valves constricted at middle; blade 

 deeply hollowed, with little calca- 

 reous material within. 



Flat and leaf-shaped, commonly with- 

 out cover-plate. 



Very diverse, both large and small. 



With sucking disc actinally, but usually 

 not abactinally. 



Usually numerous, not sunken in pits, 

 arranged in a vertical series, at inner 

 side of inner series of tube-feet, in 

 each half ambulacrum. 



Essentially triradiate, often forming 

 perforated plates. 



Usually very dark, black, olive, purple 

 or red ; sometimes light ; spines often 

 banded. 



Usually large, up to 150 mm. h. d. 



Eciiinothukid.e. 



Essentially diadematoid; some di- 

 versity shown in relative size and 

 position of plate-elements. Adoral 

 imbrication usually well-marked. 



Interambulacral plates imbricating. 



Primordial interambulacral plate re- 

 tained. Aboral imbrication more or 

 less marked. Membranous inter- 

 spaces often very marked. 



Perforated; non-crenulated. 



Large; anal system covered by nu- 

 merous small plates; anal tube 

 wanting; all oculars in contact with 

 anal system ; genito-ocular ring 

 often discontinuous; genital plates 

 often split. 



Covered by five double columns of 

 perforated ambulacral plates. 



Grooved. 



More or less inclined, with open fora- 

 men magnum. 



Continuous; auricles and apophyses 

 more or less extensively developed. 



In one, two, or three longitudinal 

 series. 



Hollow; short, usually smooth and 

 very rarely verticillate; hoofs or 

 conspicuous skin-sheaths often pres- 

 ent, at least on actinal primaries. 



Well-developed ; rarely rudimentary, 

 and possibly wanting in some in- 

 dividuals. 



Commonly well-developed. 



Long and large; oesophagus long and 

 more or less coiled. 



Wanting. 



Valves very wide near tip and deeply 



constricted, essentially as in Dia- 



dematida?. 

 Flattened and widened at tip, with 



cover-plate. 

 Very diverse, both large and small. 

 No sucking disc abactinally, and often 



not actinally. 

 As in Diadematidse. 



Usually perforated plates, often show- 

 ing triradiate origin; sometimes tri- 

 radiate spicules. 

 Deep purple, red, dull yellowish, gray, 

 or greenish; spines often banded. 



Large, 70-320 mm. h. d. 



