Introduction to Animal Morphology. 147 



no circum-oral gills, and the spines arc large and clavate ; 

 anal plates ten. 2. Salenidae extinct, (except S. rari- 

 spina), Jurassic and cretaceous forms with eleven anal plates. 

 3. Uiadematidae perforated, crenulated tubercles; spines 

 usually hollow ; the ambulacral area with perforate tubercles ; 

 peristome with notches. 4. Arbaciidae tubercles smooth, 

 imperforate ; no sutural pores ; periproct closed by four plates. 

 5. Kchinidce spine-warts and sutural pores as last ; periproct 

 of many plates ; body circular or pentagonal ; pores in three 

 orfourpairson each plate; including Temnopleurinae, with oral 

 notches shallow, and no ocular plate reaching the periproct ; 

 and Triplechinidoe, with two ocular plates reaching the peri- 

 proct, and the oral notches deeper than broad. 6. Echino- 

 metridce pores in five or six pairs ; body elliptical ; including 

 Heterocentrotus, with club-like spines ; Colobocentrotus, with 

 the dorsum of the test covered with pavement-like spines, &:c. 

 Sub-order 2. Exocyclica the anus not in the centre of 

 the apical apparatus: there are five families: i. Galeri- 

 tidce genital pores four ; ambulacra ending in an apical 

 point; including the toothless Echinoneus. 2. Dysasteridce 

 M< sozoic, with the ambulacra converging to two apical 

 points ; three anteriorly forming a trivium ; with three 

 ocular and four genital plates, two posteriorly (bivium), with 

 two ocular and no genital plate. 3. Clypeastridae ambulacra 

 iloid, often not distinct towards the margin ; mouth 

 nil, with teeth; anus inferior; spine-warts notched and 

 rate ; shell wall with duplicatures, pillars, and chambers ; 

 madreporiform plate central ; the shell may be inflated 

 and the jaws moveable on the auricles (Clypeastrmce), or 

 : thereto, and the shell flat (Laganinoe) ; the shell 

 may be lobed, or pierced by large holes, and the ain- 

 ral rows branched (Melittinoe). 4. CassiduliimUu 

 mostly cretaceous and eocene; toothless, with petaloid 

 amlitil.iera, imperforat.- and entire spine-warts; genital pores 

 terior or inferior. 5. Spatan.^uhu heart- 

 . with an anterior reniform month, and inter- 

 rupted ambulacra ; iivium embracing a sternal field; semitcu 



ma;.- nb-anal, nut perij.etalous (Kehino- 



!ium, Lovcnia), or with a peripelalous area (Hreynia) ; 



L 2 



