42 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I45 



Adoral plate arrangement. — Basicoronal plates small (text fig. 36) ; 

 adoral-most plate of interambulacrum 5 considerably larger than 

 other basicoronal plates ; paired interambulacra separated from basi- 

 coronal plates by one pair of ambulacral plates, three postbasicoronal 

 plates in each column on adoral surface ; first pair of postbasicoronal 

 interambulacral plates elongate; posterior interambulacrum in con- 

 tact with basicoronal plates; half of periproct within basicoronal in- 

 terambulacral plate ; first postbasicoronal plate of posterior inter- 

 ambulacrum extending length of lunule. 



Fig. 36. — Mellita aclinensis Kier, new species: adoral view of U.S.N.M. 

 648192, from the Tamiami formation, loc. 27. X 2. 



Aberrant specimen. — In one of the specimens the anterior ambu- 

 lacrum (III) is not fully developed (text fig. 37). The plate ar- 

 rangement is normal adoral to the tip of the petal, but there are no 

 ambulacral plates between the apical system and the tip of this petal. 

 Evidently production of ambulacral plates ceased after the first few 

 petaloid plates had been formed and the resulting gap was filled by the 

 prolongation of the interambulacral plates which would normally be 

 adjacent to this ambulacrum. 



Ontogeny. — The ambulacral lunules are not present in the smallest 

 specimen, 16.5 mm long (text fig. 38), but there are slight marginal 

 notches in ambulacra II and IV and more developed notches in V 

 and I. In a specimen 21.8 mm. long (text fig. 39) there are deep 

 notches in the paired ambulacra, with the notches in ambulacra II 

 and IV almost closed, and in a specimen 24.0 mm long (text fig. 40) 



