36 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 80 



LEPIDOCYCLINA (NEPHROLEPIDINA) DARTONI Vaughan, n. sp. 



Plate 25, figs. I, 2; plate 26, figs, i, 2, 3 



Test Stellate, six-rayed ; maximum diameter about 8.5 to 9 mm, 

 between the rays much less, probably as little as 4 mm ; rather thin, 

 thickness not certainly known, probably about 1.75 mm. Surface 

 reticulate, some rather thin, not very conspicuous, pillars, papillae 

 inconspicuous or absent. 



Embryonic chambers nephrolepidine, a smaller chamber partly em- 

 braced by a larger one. Dimensions of smaller chamber 0.4 by 0.3 mm ; 

 of larger chamber, 0.7 by 0.4 mm. In the type section there are three 

 accessory chambers, one 0.5 mm long by o.i mm wide, and two smaller 

 chambers each about o.i mm long and about half as wide. 



Equatorial chambers spatulate, those on the rays larger than those 

 in the interradial areas. The very variable size is better shown by the 

 illustrations, plate 25, figure 2, than it can be by a description. In 

 one vertical section (pi. 26, fig. 2), they are low, crowded, about 

 18 in 0.75 mm. The walls between successive layers thin. Between 

 some of the adjacent tiers there are thin pillars. 



The following is a description of the vertical section illustrated by 

 plate 26, figure 3 : 



Test tumid in the central part. Semidiameter 3 mm, total diameter 

 about 6 mm ; thickness through the center about 1.7 mm ; with a thin 

 edge about 1.5 mm wide, tapering from 0.5 mm thick on the inner 

 side to 0.2 mm thick at the periphery. Outer surface papillate, papillae 

 slightly protuberant, best developed over the center, thickness 0.1 mm 

 or somewhat more, and distant. 



Embryonic chambers comprise a central chamber partly embraced 

 by another chamber. Diameter of the apparatus in the equatorial plane 

 0.5 mm ; height, maximum 0.25 mm. 



Equatorial chambers low, near the center only 25 jx high, at the 

 periphery about 50 jx. Length near the periphery, 100 fx. 



Lateral chambers, height uniform but length very variable ; number 

 of layers on each side over the center about 1 3 ; the number decreases 

 toward the periphery to only two layers at the outer edge. The walls 

 between successive layers thin and of uniform thickness. Length 

 ranges from 0.1 to 0.3 mm. Pillars not uniformly developed between 

 all tiers of lateral chambers, some well developed, originating at the 

 embryonic or equatorial chambers and increasing in thickness toward 

 the outer surface. Maximum thickness of outer ends, a little more 

 than O.I mm. 



