STANTON : THE MARINE CRETACEOUS INVERTEBRATES. 23 



ASTARTE POSTSULCATA Sp. HOV. 

 PL V, Figs. 3-7. 



Shell of medium size, subcircular in outline, moderately convex, sub- 

 equilateral, the anterior end of the shell being slightly more prominent 

 than the posterior; beaks prominent, angular; lunule rather large, deeply 

 excavated, with abrupt walls ; surface marked by rather coarse lines of 

 growth, by occasional more prominent concentric furrows and by a broad, 

 shallow depression or furrow extending in a curve from the beak to the 

 postero-ventral margin : hinge with two well-developed cardinal teeth in 

 each valve, and both anterior and posterior laterals considerably devel- 

 oped. Margin of the shell not crenulate within. 



An average specimen measures 25 mm. in height, 26 mm. in length 

 and 1 8 mm. in convexity of the two valves. Shells of this size have 

 comparatively thick massive shells, as shown in figures 5, 6 and 7, while 

 other specimens only slightly smaller and agreeing in all other respects, 

 have very much thinner shells. This comparative thinness of test is be- 

 lieved to be due to immaturity. 



This species belongs to the same group as A. peralta, the young of 

 which it evidently closely resembles, but it may be distinguished even from 

 specimens of the same size by its much finer lines of growth, by the pres- 

 ence of the radiating posterior furrow, and by slight differences in outline, 

 especially the greater prominence of the anterior end. 



Locality and position. Represented by over 20 specimens from the 

 Ammonite (Belgrano) beds at mouth of canon four miles east of Lake 

 Pueyrrydon. 



TAPES (?) PATAGONICA sp. nov. 



PI. IV, Figs. 12 and 13. 



Shell small, rounded subquadrate, moderately convex ; beaks promi- 

 nent, situated on the anterior third of the shell ; dorsal margin excavated 

 in front of the beaks, gently convex behind them ; anterior end broadly 

 rounded, passing imperceptibly into the convex ventral margin ; posterior 

 end broad, obliquely subtruncate ; surface marked by rather coarse, regu- 

 lar concentric lines and grooves, with occasional deeper furrows, the 

 sculpture being strongest on the middle of the valve and fading out to- 

 ward the ends. There is no distinct lunule and the narrow escutcheon 

 is about half filled by the ligament. 



