150 CRETACEOUS LAMELIJlUIAXriTIA. 



1873. Cyi'kina tkapezuidalis, H. B. Geinitz. Das Elbtbalgeb. iu Saelisen 



(PalBeoutographica, vol. xx, 

 pt. 1), p. 2211, pi. 1, fig. 6 

 (?5). 



1889. Cyi-kicakdia — E. HuhapJ'd. Die Mollusk. Aacheu. Kreide 



(Palseontograpliica, vol. 

 xxxv), p. 179. 



1897. Teapezium teapezoidale, II. Wumh. Quart. Jouni. Geol. See, vol. liii, p. 



391, pi. xxviii, figs. 9, 10. 



1901. Cypeicaedia teapezoidalis, F. Shinii. Jalirb. d. k. pi-eussiscli. geol. 



Laudt'saust. fiir 1900, vol. xxi, 

 p. 80, pi. vii, fig. 5. 



1902. — — A.WollemcDui. Liiueburg. Kreide (Abhaiidl. 



d. k. preussisch. geol. 

 Laudesanst. N. F., Heft. 

 37), p. 78, pi. ii, fig. 3; 

 pi. iii, fig. 1. 



Descriplhni. — Sliell trapezoidal, rounded, inflated. Ventral margin sliglitly 

 curved, roughly parallel to the dorsal margin, and passing gradually into the 

 rounded anterior margin. Posterior margin oblique, forming an obtuse angle with 

 the dorsal margin and an acute angle with the ventral margin. Umbones near the 

 anterior end, much curved. A sharp, gently curving carina extends from the 

 umbo to the posterior angle and cuts off a triangular and slightly concave area. 



Ornamentation consists of fine concentric lines. 



Measurements ; 



Affinities. — Wollemann considers that Tra2)ezium galicianum (Favi'e)' is not 

 distinct from this species, but is founded on an older example than tlie type of 

 T. lrfijie-:oi(l(il('. According to Wollemann, various changes in the form of the 

 sliell take place during growth. Thus, iu the older specimens the valves become 

 more convex, the length relatively less, the posterior margin less oblique, the 

 ventral margin more curved, the outline less trapezoidal, and the umbones less 

 curved. This view is probably correct, l)ut none of the English examjjles which I 

 have seen pass beyond the stage represented by Eomer's type. 



Tn Trape'Mim tricarinatum (Romer)'- the umbones are less anterior in position 

 than in T. tvapczoidalc. 



1 ' Moll. Foss. de la Craio de Lemberg ' (l8l5!l), p. 109, pi. xii, tig. 3. 



- ' Die Versteiu. d. uord-deutseli. Kreidegeb.' (1841), p. 74, pi. ix, fig. 23. 



