6o2 NORTH AMERICAN INDEX FOSSILS. 



Fig. 1937- «-^, Linthia tumidula, upper, lateral, lower and posterior views, X Vz > 

 e,fy Echinocardium orthonotum, lower and lateral views, X M* (After Clark.) 



XXXIIL Maretia Gray. 

 Elongate, subpentahedral echinoids with more or less flattened 

 test ; petaloid ambulacra long and rather narrow, in shallow grooves, 

 the anterior one reduced and nearly flush; peristome small, excen- 

 tric on flat under side ; periproct on swollen posterior end, above 

 the margin. Interambulacra with comparatively coarse tubercles, 

 except the posterior one ; on the actinal side the posterior ambu- 

 lacral spaces are smooth. Eocenic-Recent. 



51. M. ruspatangus Conrad. Oligocenic. 



Anterior end with faint impression by frontal groove, dying 

 away upwards ; form slightly heart-shaped ; posterior ambulacrum 

 slightly keeled, highest point of shell being formed by it. Differs 

 from recent M. planiilata in its more truncated anterior and less 

 pointed posterior end and much greater height. Length of average 

 test, 65 mm. ; greatest width, 54.4 mm. ; height, 32 mm. 



Oligocenic of Florida and Georgia. 



XXXIV. Echinocardium Gray. 



Spatangoid, heart-shaped, swollen; ambulacra in a bivium and 



trivium, the anterior differing from the others ; paired ambulacra 



short, triangular, pointed below, unequal, divided into two unequal 



parts ; anterior ambulacra long, distinct, depressed ; anal aperture 



