678 SYSTEMATIC PALEONTOLOGY 



a distinct pattern. The typical forms are denizens of China, Japan, and 

 Korea. The two American forms which have been referred to this genus 

 by Deshayes are discussed under the head of Cyclinella, and are probably 

 allied to Mysia. They differ conchologically by having smooth inner 

 margins to the valves, a defined lunule, no trace of the fourth right car- 

 dinal tooth, and purely concentric sculpture." Ball, 1903. 1 



CYCLINA PARVA n. sp. 

 Plate XLI, Figs. 5, G 



Description. Shell porcellanous, rather heavy for its small size, sub- 

 circular in outline, moderately inflated, the maximum convexity above 

 the median horizontal; umbones subcentral, rather prominent, with fine 

 prosogyrate apices placed a little in front of the median vertical ; lunule 

 and escutcheon not differentiated ; dorsal margins obliquely truncate, the 

 anterior shorter and more gently sloping than the posterior; anterior 

 extremity broader and smoothly rounded; posterior extremity obscurely 

 truncate ; base line evenly arcuate ; external surface smooth, excepting for 

 faint concentric striations and two or three well defined resting stages, the 

 striae least feeble toward the lateral and ventral margins, but absent alto- 

 gether in the immediate vicinity of the umbones; ligament external, opis- 

 thodetic, mounted on a rather short and slender nymph ; cardinals three 

 in number in each valve, radiating fan-like from beneath tin- umbones, 

 the anterior cardinal in the right valve thin, laminar and somewhat pro- 

 duced, the middle cardinal stouter, widening ventrally, the posterior 

 obliquely produced and asymmetrically bifid; anterior and medial car- 

 dinal of the left valve united beneath the umbones, the anterior slender, 

 laminar, elongated, the medial shorter, slightly elongated and stouter, the 

 posterior very slender and not very much produced ; adductor scars rela- 

 tively large, narrow but elongated, placed well up near the extremities of 

 the hinge line; pallial sinus distinct, acutely angulated at about 90, the 

 breadth and depth approximately equal; pallial line distant; inner ven- 

 tral margins simple. 



1 Trans. Wagner Free Inst. Sci., Phila., vol. iii, pt. vi, p. 1234. 



