40 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 149 



these smaller specimens (pi. 9, fig. 1) the periproctal opening is not 

 visible from the adoral side. The opening is lower on the larger tests 

 and the truncation is tilted so that the opening is partially visible from 

 the adoral side on a specimen 71 mm. long (pi. 9, fig. 3), and com- 

 pletely visible on a full-size adult (pi. 9, fig. 4) . 



MM. 

 1401 



-120 



£100-1 



80- 



^ 60- 

 § 40 



UJ 



X 



20- 







+ 

 + + 



© © 



+♦ 



o % 



20 40 



60 80 

 LENGTH 



100 120 

 OF TEST 



—i r 



140 



160 



MM. 



Fig. 8. — Meoma ventricosa (Lamarck). Scatter diagram showing rates of 

 increase in height and width of test as length increases. 



The dorsal posterior surface of the smallest specimen is highly in- 

 flated (pi. 9, fig. 1), but on larger specimens (pi. 9, figs. 3, 4) it is 

 depressed and slopes steeply posteriorly. Anteriorly the situation is 

 reversed, with the front steep in the smallest specimen, but more 

 gently sloping in the larger. 



Petals. — One of the most striking differences between small and 

 large Meoma ventricosa is in the relative length of the posterior petals. 

 In the smallest specimen available (pi. 9, fig. 1), 22 mm. long, 

 the posterior petals extend only one-half the distance from the 

 apical system to the margin, whereas in a specimen 144 mm. long (pi. 

 9, fig. 4), they extend 83 percent of this distance. A scatter diagram 



