294 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Sculpturing of test more or less well marked; madreporic genital 



with 10-15 pores or more; no sexual dimorphism Trigonocidaris. 



Sculpturing of test slight or wanting; madreporic genital with only 

 2 or 3 large pores; marked sexual dimorphism; abactinal system 



of female greatly elevated and modified Hypsiechinus. 



Actinostomal membrane naked, at least outside the ring of buccal plates 



which are usually conspicuous. 

 Periproct more than half covered by a single plate; actinostomal 



membrane with only the buccal plates Genocidaris. 



Periproct not half covered by any one plate; peristomal membrane 



with at least a few plates proximal to the buccal circle. 

 Periproctal plates few, large, and more or less glassy. 



Actinostomal membrane with few plates proximal to the 

 buccal circle; coronal plates usually with distinct sculp- 

 turing; ocular plates more or less swollen and genitals 



usually more or less sculptured Orechinus. 



Actinostomal membrane well plated within circle of buccal 

 plates; coronal plates only faintly sculptured; ocular 

 and genital plates flat, smooth, and not sculptured . . Lamprechinus. 



Periproctal plates numerous and not glassy Prionechinus. 



Sculpturing of test consists of a series of depressions along horizontal inter- 



ambulacral sutures; there are 4-6 of these on each suture at ambitus . . Opechinus. 

 Test not sculptured (or rarely so) but with pits on horizontal sutures or at angles 



of coronal plates; latter united by dowelling TEMNOPLEDRIN^B. 



Primary tubercles distinctly crenulated. 



Coronal plates, at least abactinally, with deep and more or less conspicu- 

 ous pits at their sutural angles; these pits are usually extended more 

 or less distinctly along the horizontal sutures; each interambulacral 

 plate at ambitus with 1 or 3 (very rarely 4) primary tubercles . . . Temnopleurus. 

 Coronal plates usually with small sutural pits or none; if the pits are large 

 enough to form a furrow along the horizontal suture, the inter- 

 ambulacral plates at ambitus each carry 4-9 subequal primary 



tubercles in a horizontal series Salmacis. 



Primary tubercles small, not crenulated (faintly so in some large specimens). 

 Every ambulacral plate with a primary tubercle close beside the porif- 

 erous area. 



Coronal plates with deep, conspicuous, usually oblong pits at the 

 sutural angles and on their horizontal sutures; poriferous areas 

 narrow, the pore-pairs in an approximately vertical series . . . Temnotrema. 

 Coronal plates with small sutural pits or none. 



Median abactinal interambulacral areas (and usually ambulacral 

 also) more or less extensively bare and free from spines 

 and tubercles. 



Interambulacral plates low and numerous (21 or 22 in each 

 column in specimens 20 mm. h. d.)i pore-pairs dis- 

 tinctly biserial Mespilia. 



Interambulacral plates high and few, not more than 18, 

 even in largest specimens (25 mm. h. d.); pore-pairs 

 usually'monoserial . 



