COMPENDIUM OF GENERIC DISTINCTIONS. 



80 1 



GfHus. PSOLUS. Body irregular, slug-like. Tentacles ten. 



Family. PENTACTADJE. Suckers in five regular rows. 

 Body irregular. 



Genus. PBNTACTA (includes CUCUMARIA). Suckers alter- 

 nate in each row, close. Tooth-plates nearly square. Tenta- 

 cles ten. 



Genus. PSOLINUS. Body curved. Suckers distinct from 

 each other. Under-suckersbent. Teeth short. Tentacles ten. 



Family. SYNAPTAD^E. Suckers none. 

 Genus. SYNAPTA. Body cylindrical, slender, long. Ten- 

 tacles long, and fingered at tips. 



Order. ECHINOIDEA. Shell chalky, either spherical 

 or disc-like, formed of immovable plates. Locomotion by 

 spines and suckers. 



Family. CIDARIDiE. Body globular. Mouth above and 

 vent below, in centre of body. Five unbroken avenues. 

 Teeth complicated. 



Genus. ECHINUS. Spines of same form, the knobs of shell 

 not perforated. 



Genus. CIDARIS. Spines of several forms ; knobs of shell 

 perforated. 



Family. SPATANGID-iE. Mouth below, not in centre. 

 Vent at one side. Avenues not continuous. Teeth wanting. 



Genus. SPATANGUS. Body heart-shaped, flattened. Ave- 

 nues above and below. No dorsal impression. 



Genus. AMPHIDOTUS. Body heart-shaped, convex. An 

 impression in four of the dorsal avenues. 



Genus. BRISSUS. Body heart-shaped, convex, dorsal im- 

 pression enclosing avenues. 



Family. CLYPEASTERIDJE. Mouth and vent both 

 below ; mouth in centre, toothed. Avenues not continuous. 



Genus. ECHINARACHNIUS. Body nearly circular, very flat, 

 edge nearly entire. Avenues short. Vent between mouth 

 and hinder edge. 



Genus. ENCOPB. Body flat, nearly circular, lobed and 

 pierced with keylike-shaped holes. South America. 



Genus. ROTULA. Body flat, front of disc cut into deep 

 teeth ; hinder edge not lobed, nearly entire. South America. 



Sub-class. HVPOSTOM ATA. Stomach sac-like, only 

 one aperture. Body lobed or rayed. 



Order. ASTEROIDEA. Shell composed of many mov- 

 able pieces. Skin sometimes leathery, sometimes calcareous. 

 Digestive canal symmetrical. 



Family. ASTERIAD^E. Rays developed from body. 

 Locomotion by suckers under rays. 



Genus. ASTERIAS. Body star-shaped. Rays flattish and 

 short, edged with plates. Avenues edged with three sets of 

 spines, two rows of suckers in each avenue. 



Genus. URASTER. Body rather conical, rays rounded, two 

 rows of suckers in each avenue, and three sets of spines. 



Genus. GCNIASTER. Body conical, edged with spiny 

 plates. Avenues edged with cross rows of spines. 



Genus. ASTERIN.*. Body covered with short spines on 

 both surfaces. Avenues edged with a single row of spines. 



Genus. PALMIPES. Body flat, thin, with small tuft of 

 spines. Avenues edged by longitudinal tufts of spines. 



Genus. SoLASTER. Many rays, covered with tufts of 

 spines. Avenues edged with three sets of spines, and furnished 

 with two rows of suckers. 



Genus. CRIBELLA. Rays few, covered with spiny tuber- 

 cles. Avenues edged with two sets of spines. 



Family. OPHIURID^E. Rays long, affixed to round disc 

 like the body of an Echinois. Locomotion by suckers. 



Sub-family. OPHIURINA. Rays simple. 



Genus. OPHIURUS. Rays scaly, prolonged at disc. Large 

 shield-like plates at origin. Threads between spines simple. 



Genus. OPHIOCOMA. Rays scaly, not prolonged at disc. 

 Small pentagonal plates at 'origin. Threads between spines 

 pinnate. 



Sub-family. EURYALINA. Rays much branched. 

 Genus, ASTROPHYTON. Rays repeatedly two-branched. 



5 



Order. CRINOIDEA. Digestive canal not symmetrical. 

 Chalky shell formed of many movable pieces. 



Genus. COMATULA. Rays five, pinnate. When adult, 

 free ; when young, seated on stern. 



Genus. PENTACRINUS. Permanently on long_ footstalk, 

 which is pentagonal and formed of numerous joints. Fila- 

 ments placed in whorls on footstalk, which does not alter in 

 diameter. Warm seas. 



CLASS ACALEPHA. 



Radiate, gelatinous, free A digestive cavity with ra- 

 diating vessels Poison-threads Metamorphosis. 



Order. SIPHONOPHORA. Body irregular. Nocentral 

 digestive cavity. With sucking organs. Locomotion by con- 

 tractile cavity or sacs filled with air. 



Family. VELELLAD^E. Animal stretched over gristly 

 plate. 



Genus. VELELLA. Body flat, oval. Oblique crest above ; 

 tubular mouth below, surrounded by short tentacles. 



Family. PHYSALIADJE. Animal a large air-filled sac, 

 with many tentacles. 



Genus. PHYSAUA. Air-sac large, oblong, crest-wrinkled. 

 Tentacles near one end, long, variously-shaped. 



Family. DIPHYID^E. Animals bell-shaped, double, 

 fitting into each other. 



Genus. DIPHYES. Animals pyramidal, a few points round 

 aperture. 



Order. CTENOPHORA. Body symmetrical, not disc- 

 shaped. Large central digestive cavity. Locomotion by par- 

 allel rows of cilia. 



Family. CALLIANIRID^E. Two long, contractile fila- 

 ments in chambers, one on each side. 



Genus. CYDIPPE. Body globular, no lobes nor tentacles. 



Family. BEROID^E. No contractile filaments nor 

 chambers. 



Genus. CESTUNS. Body very flat, wide, and short, edged 

 with cilia. Hot seas. 



Order. DISCOPHORA. Body disc-shaped, oval, or less 

 convex. Large central digestive cavity. Locomotion by ex- 

 panding and contracting disc. 



Tribe. GYMNOPTHALMA TA .Eye-specks uncovered 

 or wanting. Circulating vessels running to margk, either sim- 

 ple or branched. 



Family. SARSIADjE. Vessels simple, four. Ovaries in 

 substance of footstalk. 



Genus. SARSI A .Hemispherical; four tentacles at edge of 

 vessels. Eye-specks four. Stomach in extensile footstalk. 



Family. WILLSIAD^E. Vessels branched. 



Genus. WILLSIA Globular. Ovaries six. Vessels six. 

 Eye and tentacle opposite each branch. Footstalk short. 



Family. ,<EQUOREAD/E. Vessels more than eight. 

 Disc flattish. Ovaries in a line along vessels. 



Genus. ^EQUOREA. Disc rather onvex. Vessels very 

 numerous. Footstalk wide, cleft into many broad lobes. Ten- 

 tacles slender. 



Genus. EUDORA. Disc very flat. No tentacles nor foot- 

 stalk. Hot seas. 



Trtbe. STEGAtfOPTIfALllfATA. Eyt-sptcks cov- 

 ered by flaps. Circulating vessels forming a network. 



Family. MEDUSAD^E. Stomach with a mouth, through 

 which solid food is taken. 



Genus. CHRYSAORA. Disc hemispherical, lobed. Many 

 tentacles on edge. Four very long fwbelowed arms, not 

 fringed. 



Genus. MEDUSA. Disc hemispherical. Many tentacles on 

 edge. Eyes eight. Ovaries, chambers, and fringed arms 

 four ; one opening in centre, four at sides. 



Genus. CYANEA. Disc flattened, rather scalloped; four 

 fringed arms. Tentacles of edge very numerous, set beneath 

 disc. 



