SYSTEMATIC DESCRIPTIONS SPATANGINA. 53 



Key to the West Indian Fossil Genera of Spatangina . 



1. Interambulacra all approximately alike orally, so that there is no sternum developed, 



even when the mouth is anterior. 

 A. Ambulacra not petaloid; test more or less depressed, peristome oblique. 



Test elongate, oval in marginal outline Echinoncus 



Test nearly or quite circular in marginal outline. Amblypygus 



AA. Ambulacra all more or less petaloid. 



B. All ambulacra petaloid or subpetaloid abactinally. 



Periproct higher than wide, marginal Parapygus 



Periproct wider than high, submarginal Echinolampas 



BB. Ambulacrum III conspicuously different abactinally from other ambulacra, which 

 are broadly petaloid. 



Ambitus oval or elliptical; petals not tending to close at ambitus Asterostoma 



Ambitus subcircular; petals closing at ambitus Pseudasterostoma 



2. Interambulacrum 5 conspicuously different orally from the others, forming the so-called 



sternum. 

 A. Apical system elongate; genitals 2 and 3 meeting in mid-line, but separated from 

 genitals 1 and 4 by oculars II and IV, only a marginal fasciole 



present Cardiaster 



AA. Apical system not as above. 



B. No true subanal fasciole, but a lateroanal fasciole is frequently present. 



C. Peripetalous fasciole wanting anteriorly as it passes, on side of test, into a mar- 

 ginal fasciole which runs below the ambitus both anteriorly and 

 posteriorly. 

 Ambulacra II and IV scarcely petaloid dorsally, the anterior series of pore-pairs 



in each are greatly reduced or wanting Agassizia 



Ambulacra II and IV petaloid; anterior series of pore-pairs normal Prenaster 



CC. Peripetalous fasciole complete; no marginal fasciole. 



D. Abactinal system ethmophract; no lateroanal fasciole; genital pores 4. . Hemiaster 

 DD. Abactinal system ethmolytic. 



E. Genital pores 4; lateral petals not deeply sunken. 



Petals I and V much shorter than II and IV; test very wide Paraster 



Petals I and V about as long as II and IV; test narrower Periaster 



EE. Genital pores 2 or 3; all petals deeply sunken Schizaster 



BB. Subanal fasciole present. 



F. No internal fasciole. 

 G. Petals, at least the paired ones, deeply sunken. 



H. Ambulacrum III more or less petaloid, sunken Brissopsis 



HH. Ambulacrum III not petaloid. 



I. A distinct anal fasciole present Plagiobrissus 



II. No anal fasciole. 



Ambulacrum III sunken so that the ambitus is concave anteriorly, 



often deeply so Macropneusles 



Ambulacrum III flush, ambitus anteriorly more or less convex. Brissus 



GG. Petals flush Eupatagus 



FF. Internal fasciole present Breynia 



Of the genera of the Spatangina found fossil in the West Indies, 



the following number of fossil species have been recognized : 



Under Echinoneus 2 fossil species (see Key, p. 54). 



Under Amblypygus only 1 fossil species, Amblypygus americanus. 



Under Parapygus 2 fossil species (see Key, p. 56) 



Under Echinalampas 7 fossil species (see Key, p. 57). 



Under Asterostoma 2 fossil species (see Key, p. 67). 



Under Pseudasterostoma only 1 fossil species, Pseudasterostoma jimenoi. 



Under Cardiaster only 1 fossil species, Cardiaster cubensis. 



Under Agassizia 2 fossil species (see Key, p. 70). 



Under Prenaster only 1 fossil species, Prenaster loveni. 



Under Hemiaster 4 fossil species (see Key, p. 73). 



Under Paraster 5 fossil species (see Key, p. 75). 



Under Periaster only 1 fossil species, Periaster elongatus. 



Under Schizaster only 1 fossil species, Schizaster scillce. 



Under Brissopsis 3 fossil species (see Key, p. 81). 



Under Plagiobrissus only 1 fossil species, Plagiobrissus loveni. 



